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V 


RADIO-TELEGRAPHY 


























RADIO¬ 

TELEGRAPHY 


BY 

C. C. F. MONCKTON, M.I.E.E. 



NEW YORK 

D. VAN NOSTRAND COMPANY 
23 MURRAY AND 27 WARREN STREETS 

1908 


















, * 

I > 


! 






BRADBURY, AGNKW, & CO. LD., PRINTERS, 
LONDON AND TONBRIDGE. 



0 ? 





PREFACE 

It is hoped that this book may serve a useful purpose in 
enabling readers to become acquainted with the principles 
and practice of radio-telegraphy. Some knowledge of 
electricity is essential, and, though it is impossible to 
thoroughly understand the phenomena without much 
handling of electric apparatus, an attempt is made in the 
first chapter to state as simply as possible the fundamental 
facts relating to electricity and magnetism; for until these 
are grasped it is hopeless to try to appreciate the mechanism 
of radiant waves. In the next two chapters electric vibra¬ 
tions are first explained, and then the fundamental pheno¬ 
menon of radio-telegraphy, the radiation of energy from a 
vibrating electric circuit. 

Hertz, who proved experimentally the existence of these 
radiant waves, worked for science and not for telegraphy. 
It remained for a host of inventors to adapt the newly- 
discovered phenomena to practical use. The waves, with 
which Hertz himself experimented, were too small, and in 
Chapter IY. the properties of the modified longer waves, 
used in practice, are enumerated. In Chapter Y. a descrip¬ 
tion of the power plant for making the electric vibrations is 
given; Chapters VI. and VII. deal in detail with the wave 
transmitter, and Chapters VIII. and IX. describe the wave 


VI 


PREFACE. 


receiver. Measurements, requiring the use of mathematical 
formulae, follow in Chapter X. In the three following 
chapters are described typical stations, using respectively 
the single vibrating transmitter of Lodge, the coupled 
circuits of Braun, and the hydrogen arc of Poulsen. The 
self-imposed vow of secrecy on the part of the Marconi 
Company alone prevents a description of one of their 
mammoth stations. In Chapter XIY. portable stations are 
briefly touched on, and the last chapter deals with the 
latest technical development—radio-telephony. 

In the Appendix will be found the Morse alphabet, a list 
of electrical units used, and a resume of the articles of the 
International Radio-telegraph Convention of 1906, with 
service regulations. 

Large sums of money have been spent experimentally in 
bringing radio-telegraph apparatus to its present state of 
efficiency, so to-day the cost of erecting a station is often 
largely increased by sums for patent rights. Unfortunately 
it is not known how far many of the patents of the different 
companies are valid, and how far each com})any infringes 
on the rights of other companies. It is this question of 
patent rights that is no doubt preventing a more rapid 
increase in the number of radio-telegraph stations, but, con¬ 
sidering that it is only twelve years since the first practical 
applications, the progress has been enormous. 

A short time back it seemed possible that future pro¬ 
gress might be prevented by a radio-telegraphic war. The 
Marconi Company had practically obtained a monopoly in 


PREFACE. 


Vll 


England; they had erected numerous stations along the 
coasts and on the Atlantic liners, at the same time refusing 
to intercommunicate with stations fitted with apparatus not 
supplied by them. On the other hand, a powerful com¬ 
peting company had sprung up in Germany, the combina¬ 
tion of four interests (Slaby, Arco, Siemens, and Braun), 
and it is likely that either company might have so filled 
space with a medley of discordant waves as to effectually 
prevent the other working. Happily, though the com¬ 
panies were unable to come to an understanding, the 
Governments of all the principal countries in the world 
have made a satisfactory agreement, the terms of which 
come into operation on the 1st July, 1908. By the terms of 
the Convention intercommunication is compulsory between 
a ship and a coast station, except for those especially to be 
exempted. Interference with other stations as far as 
possible is prohibited, and priority is to be given to calls 
from ships in distress. Most of the principal countries, 
with the exception of Great Britain and Italy, have also 
agreed to compulsory intercommunication between ship 
and ship stations. 

Service regulations have been drawn up which fix under 
ordinary conditions the wave-lengths to be employed. The 
telegraphist on a ship station must hold a certificate as to 
his technical proficiency issued by the Government to whose 
authority the ship is subject. The charges to be levied are 
fixed, and an international bureau will have the duty of 
publishing information of every kind relative to radio- 


Till 


PREFACE. 


telegraphy, besides circulating proposals for modification 
of the Convention and regulations. 

The conference of 1906 not only regulated the service; 
it fixed the name of the new method of intercommunica¬ 
tion, which previously had been called “ Wireless Tele¬ 
graphy ” in England and “ Spark Telegraphy ” in Germany. 
It had been proposed to call it “ Hertz Telegraphy ” (after 
the discoverer), but it has now been definitely named 
“ Radio-telegraphy; ” and the -message received is to be 
called a “ Radio-telegram,” a word which before long will 
probably be shortened to “ Radiogram.” 

The British Admiralty were the first to make practical 
use of Hertz’s discovery, and the high state of perfection of 
the apparatus used is largely due to the initiative of the 
present controller of the Admiralty, Rear Admiral Sir H. B. 
Jackson. Fortunately for the future security of our empire, 
the latest improvements are kept a profound secret. In 
1905 the system was sufficiently perfect for a ship to receive 
signals from a station 180 miles away on one mast, and at 
the same time, from a mast 200 feet distant, messages could 
be sent to another station fifty miles away. The great 
importance of this new means of communication in naval 
warfare was amply demonstrated in the war between Japan 
and Russia. 

The business man, whilst travelling between England 
and America, is now able to keep in touch with his affairs, 
and there are few important passenger steamers that are 
not fitted with its radio-telegraph station. 


PREFACE. 


IX 


At an early date Lloyds saw the importance of this new 
means of communication for ships in distress, and they have 
.now numerous stations in operation. 

A new field has been opened for radio-telegraphy in loca¬ 
ting a given direction during a fog, and this method is being 
developed with considerable success by Marconi and others. 

So far radio-telegraphy has been chiefly utilised between 
ship and ship, or ship and shore. In these fields it has no 
rival. For land service it has the serious competition of 
the telegraph and telephone, whilst from shore to shore the 
submarine cable has not yet been ousted. 

For military operations radio-telegraphy will certainly be 
largely used. The Japanese employed it successfully in 
their last war, and the besieged garrison in Port Arthur 
kept up constant communication with China by its means. 
Great portability of apparatus and aerial have been attained. 

For land working it is also employed in the Arctic regions, 
where snow makes the upkeep of land-lines almost impos¬ 
sible, and it might sometimes be used with advantage in 
the tropics along the coast, where rank vegetation makes 
the upkeep of telegraph or telephone lines costly and 
troublesome. 

For sbore-to-sliore stations radio-telegraphy has the 
advantage over the submarine cable in that no repair ship 
is required, and the initial cost is comparatively small. At 
present, however, the speed of working is considerably less 
than with the cable, and there is slightly more liability to 
interference from atmospheric disturbances. Increased 


X 


PREFACE. 


speed of working is one of the principal problems of radio¬ 
telegraphy. With the tape about fifteen words can be 
recorded a minute, whilst about thirty words in Morse 
signals can he received through the telephone; in cable¬ 
working, on the other hand, as many as one hundred words 
a minute can be received on the tape and read by a skilled 
operator. 

Atmospheric disturbances were a great source of trouble 
in the early days before syntonic working was introduced. 
Using a close coupling in the receiver, the author has 
noticed almost a continuous record of signals due to this 
cause. At the same station with good syntony and a 
loose coupling signals can now be always read except 
during a severe storm. It is probable these disturbances 
can only be completely eliminated by using continuous 
waves or an extremely weak coupling. 

At present the choice of system to he used is governed by 
a large number of factors, such as initial expenditure, cost 
of upkeep, skill of operators, liability to interfere with other 
stations, and liability to interference from other stations. 
In the author’s opinion, no one system can be called the 
best; the system to be used should depend on the special 
circumstances. 

One problem outstanding is radio-telephony. Progress 
is being made at a very rapid rate. 

The problem of the immediate future is commercial 
inter-communication between Great Britain and America. 
In his lecture, recently given before the Royal Institution, 


PREFACE. xi 

Marconi gave the date of his first transatlantic signal 
received as December, 1901. The wave-length has been 
increased from 1,200 feet to 2,600 feet, and again to 
12,000 ; since the completion of his latest arrangements 
up till February of this 3 7 ear 119,945 words of press 
and commercial messages were transmitted across the 
Atlantic. Before many months it is hoped that Poulsen 
will have made the attempt of transatlantic signalling by 
means of the radio-telephone with the 10 h.p. of radiated 
energy, which he considers all that is required. 

For supplying information and illustrations of their 
apparatus, my thanks are due to the leading manufac¬ 
turers, Messrs. The Amalgamated Radio-Telegraph Com¬ 
pany, Messrs. Die Gesellschaft fur Drahtlose Telegraphie, 
Messrs. The Lodge-Muirhead Wireless and General Tele¬ 
graphy Syndicate, Messrs. Marconi’s Wireless Telegraph 
Company, Messrs. The Cambridge Scientific Instrument 
Company and Mr. H. W. Sullivan. The proprietors of 
Electrical Engineering have also kindly lent a number 
of illustrations, and Mr. J. H. Carson, manager of the 
Anglo-American Telegraph Company, has supplied me with 
the telegraphic abbreviations used by his company. 

More especially are my thanks due to my friend, Mr. 
Arnold G. Hansard, M.I.E.E., for numerous suggestions 
and criticisms. 

C. C. F. M. 

London, 

March 23rd, 1908. 



TABLE OF CONTENTS 


PAGE 

Preface . v 


CHAPTER I. 

ELECTRIC PHENOMENA. 

Electricity—Conductors and insulators, dielectrics—A few properties 
of charged bodies—The electric field—Electric intensity—Lines 
of force — Tubes of force — Potential — Capacity — Condensers — 
Electric displacement—Magnetism—Magnetic displacement, or 
induction—Polarisation—Electro-statics and Electro-magnetics— 
Electric currents—Production of electric currents—Resistance 
and penetration of currents in conductors—Uniform conduction 
current—Electro-motive force—Electric inertia or self-induction 
—Mutual induction—Relation between electricity and magnetism 
— Energy — Units — Dimensions of electric quantities . . p. 1 


CHAPTER II. 

ELECTRIC VIBRATIONS. 

Vibrations—Damping—Nodes, antinodes and harmonics—Energy of 
vibrations — Interference. Svntony—Phase — Mass and com¬ 
pliancy of vibrating string—Electric vibrations—Oscillation con¬ 
stant—Stationary waves—Secondary electric vibrations—Velocity 
of moving charges along wires—Methods of producing secon¬ 
dary vibrations — Method of examining electric vibrations in 
wires . . . . . . . . . . . p. 25 


XIV 


TABLE OF CONTENTS. 


CHAPTER III. 

ELECTRO-MAGNETIC WAVES. 

History —Waves —Telocity of propagation : frequency and wave¬ 
length—Amplitude of wave disturbances—The vibrating receiver 
—Electro-magnetic waves—Hertz's experiments—Closed tubes of 
electric force—Representation of electro-magnetic wave striking 
a Hertz resonator—The magnetic field—A method of depicting 
the electric and magnetic fields—Representation of a train of 
waV es—The medium through which electro-magnetic waves are 
propagated—Comparative duration of vibrations—'Wave-length 
of light compared with that of Hertz, and the waves used 
in practical radio-telegraphy—The two forms of electric oscil¬ 
lator . . . . . . • . • • . p. 42 


CHAPTER IV. 

MODIFIED HERTZ WAVES USED IN RADIO-TELEGRAPHY. 

History—The Marconi Aerial—Earthing the aerial—Theory of earthed 
Hertzian waves—Pierce’s experiments—Hr. Erskine Murray’s 
hypothesis—Free Hertzian waves—Earthed waves with surface 
not perfectly conducting—The radiated magnetic waves—Obstruc¬ 
tions, inequalities, and curvature of the earth—Experiments on 
the screening action of obstructions—Trees as aerials—Dissipa¬ 
tion of energy due to light—Dissipation of energy due to con¬ 
ducting particles in the air — Energy received — Distance of 
transmitting signals — Difficulties of signalling at dawn and 
sunset . . . . . . . . . . p. 60 


CHAPTER V. 

APPARATUS USED FOR CHARGING THE OSCILLATOR. 

History—The induction coil—Rating of induction coils—The Tele- 
funken induction coil—The interrupter — Apparatus used for 
working induction coils — Arcing between spark-knobs—The 
Lodge valve—Alternate current transformer—The Lodge-Muir- 
head transformer and alternator—High power apparatus—Pro¬ 
tection of apparatus—The musical arc —The Cooper-Hewitt 


TABLE OF CONTENTS. 


xv 


mercury interrupter as a radio-telegraph discharger—Vreeland’s 
modification of the mercury interrupter—The high frequency 
alternator—The spark or arc, in compressed air . . . p. 76 


CHAPTER YI. 

THE ELECTRIC OSCILLATOR—METHODS OF ARRANGEMENT. 

History—Systems of transmitting—Single aerial or antenna—Dis¬ 
advantages of the single aerial—Aerial loaded with capacity— 
Coupled systems—The radiating circuit—Methods of coupling— 
Damping of vibrations in radiating circuit—The principal wave 
of a vibrating circuit—Limitations of close coupling—Coupled 
circuits compared with open circuits—The auto-transformer— 
The Tesla transformer—The auto and Tesla transformer compared 
—Couplings for high power stations—System of directed waves 
by means of horizontal wires—-Braun’s system of directed waves 
— The directive system of Bellini and Tosi. . . . p. 94 


CHAPTER YIL 

THE ELECTRIC OSCILLATOR—PRACTICAL DETAILS. 

The aerial—Earthing the aerial—Protection from lightning—Variation 
of effective spark length with capacity—Characteristics of the 
oscillatory spark—Potential difference required to produce a dis¬ 
ruptive discharge—Multiple spark-knobs—Material of spark- 
knobs and density of dielectric—Position of spark-gap—Arcing — 
Coupled circuits—Transmitting key—Auto-transmitter—Arrange¬ 
ment of apparatus—The Poulsen arc—Marconi’s transatlantic 
practice . . . . . . . . . . p. 119 


CHAPTER VIII. 

THE RECEIVER—METHODS OF ARRANGEMENT. 

History—Method of receiving radio-telegraphic signals—The receiving 
transformer—Auto-transformer—Importance of syntony—Advan¬ 
tages of using a secondary circuit—Shunted capacity to the 
coherer—Damping in the receiving circuits—Subsidiary circuits— 


XVI 


TABLE OF CONTENTS. 


Belay and tapping circuits with coherer—Syphon recorder and 
clockwork with coherer—The overflow arrangement of Lodge— 
Receiving circuits compared—Changing from receiving to sending 
—The Poulsen-Pedersen arrangement . . . . p. 145 


CHAPTEB IX. 

THE RECEIVER—THE DETECTING APPARATUS AND OTHER DETAILS. 

History —The function of the detector — Difference of potential 
detectors—Theory of the coherer—Branly’s coherer—The Lodge- 
Muirhead coherer—Auto-coherers—The audion of De Forest— 
Current detectors — The magnetic detector — The electrolytic 
detector—The lead peroxide detector of Brown—Fessenden’s 
barretter—The microphonic detector—Thermo-electric detectors — 
The carborundum detector—The telephone receiver—Potential 
versus current detectors—Testing the detector—Regulation of local 
circuit — Calling-up arrangement — Sullivan’s relay — Practical 
details ..... . .... p. 163 


CHAPTER X. 

MEASUREMENTS IN RADIO-TELEGRAPHY. 

Subsidiary apparatus — Ammeter in sending circuit — Ammeter in 
receiving circuit—Method of finding best coupling in sending 
circuits—The currents in oscillatory circuits—Use of ammeter in 
subsidiary circuit—Measuring instruments used in the transmitter 
—The thermo-galvanometer—The bolometer— The high frequency 
dynamometer—Wave measurement—The theory of wave measure¬ 
ment—Resonance curves—Resonance curves of coupled circuits— 
Damping—The damping curve—Damping of compound oscilla¬ 
tions— Comparison between the damping of closed and open 
circuits—Ohmic resistance of wires—Number of oscillations in a 
train of waves—Number of trains of waves per second . p. 186 


CHAPTER XI. 


THE EXPERIMENTAL STATION AT ELMERS END — LODGE-MUIRHEAD 
SYSTEM. p. 215 


TABLE OF CONTENTS. 


XVII 


CHAPTER XII. 

RADIO-TELEGRAPH STATION AT NAUEN—TELEFUNKEN SYSTEM }>. 225 


CHAPTER XIII. 

THE RADIO-TELEGRAPH STATION AT LYNGBY—POULSEN SYSTEM ]>. 232 


CHAPTER XIV. 

PORTABLE STATIONS. 

The Lodge-Muirkead system. — The Marconi system—Telefunken 
system—Poulsen system . . . . . . . p. 240 


CHAPTER XV. 

RADIO-TELEPHONY. 

Ruhmer’s discovery — Fessenden’s system of radio-telephony — The 
Telefunken system of radio-telephony—Other systems . p. 249 


Appendix A —The Morse Alphabet . . . . . . p. 257 

Appendix B—Electrical Units used in this Book . . . />. 259 

Appendix C—International Control of Radio-Telegraphy . p. 260 

p. 265 


Index 



































































RADIO-TELEGRAPHY. 


CHAPTER I. 

ELECTRIC PHENOMENA. 

Electricity .—It is a well known phenomenon that 
when a piece of sealing wax is rubbed against a 
piece of dry flannel both of these substances acquire 
a state by which they attract light bodies, these 
bodies being repelled immediately after contact. The 
sealing wax, flannel, and light bodies are said to have 
become charged with electricity or to have charges of 
electricity. There is a force of attraction between the 
charged sealing wax and the flannel, hut two pieces of 
charged sealing wax will repel one another, and so also will 
two pieces of charged flannel. The flannel is said to be 
positively charged, the sealing wax negatively charged. 
Positively charged bodies always repel one another, nega¬ 
tively charged bodies always repel one another, hut between 
]x>sitively and negatively charged bodies there is always a 
force of attraction. The actual charges of electricity are 
also attracted or repelled in like manner, and when two 


R.T. 


B 




o 


RADIO-TELEGRAPHY. 


oppositely charged bodies are brought sufficiently close 
together the strain may become so great that a dis¬ 
ruptive discharge of electricity, in the form of a 
spark, takes place between the bodies, and in general 
the bodies are no longer electrified; but under certain 
conditions they are recharged, but each in the oppo¬ 
site sense to its previous state; and, just as when a 
weight is swung it overshoots its final position of rest 
and swings backwards and forwards, so the two charges 
may swing backwards and forwards, a spark taking place 
at each swing. Under these special conditions of oscillatory 
discharge this disruptive spark had been till 1906 the only 
practical method of signalling by radio-telegraphy ; in fact 
the name spark telegraphy was proposed as more suitable 
than the old name wireless telegraphy. 

Conductors and Insulators, Dielectrics .—A material is a 
conductor when it allows its charge to be quickly given up 
to another body, or is quickly charged when brought into 
contact with an electrified body. An insulator or dielectric, 
on the other hand, gives up its charge slowly. In a wireless 
telegraph station the conductor used is copper. The earth, 
salt water, and growing vegetation play an important role 
as conductors between the sending and receiving stations. 
The insulators used are air, porcelain, glass, ebonite, mica, 
paraffin wax, india-rubber, and silk. When the isolation 
of electric charges is being dealt with the term insulator is 
used ; on the other hand, when storage of energy is being 
discussed, the correct word is dielectric; but it must be 


ELECTRIC PHENOMENA. 


3 


remembered that a good insulator is always a good dielectric, 
and vice versa. 

A few Properties of Charged Bodies .—The charges on 
conducting bodies are on the surface. By means of special 
apparatus it is possible to measure the charge, that is, the 
quantity of electricity on a body. 

The density of the charge over the surface of a body, 
that is, the charge per unit of surface, varies inversely as 
the radius of curvature. The surface density thus becomes 
relatively very large at points, 
causing a brush discharge if 
the bodies are highly charged. 

If an insulated conductor A 
(Fig. 1) be brought near to 
a charged body B the total 
charge, if any, on the con- 
ductor remains as before, but 

the portion of the conductor A near the body B becomes 
charged in an opposite sense; that far away in the same 
sense as the body B. Along one line round the conductor 
there is no electricity ; the charge gradually increases from 
this line in both directions, but in opposite senses, as 
shown diagrammatically by the size and thickness of the 
4- and — signs. If the conductor A be now touched by 
another conductor it will be left with a charge opposite 
in sign to that on B. This is called electrification by 
induction. Machines to generate electricity by this means 
are called influence machines. 

b 2 



4 


RADIO-TELEGRAPHY. 


When electricity is excited by any means the charges of 
positive and negative electricity produced are always equal. 

The force exerted by two small charged bodies on each 
other, if far apart, is proportional to the product of their 
charges and inversely proportional to the square of the 
distance between them. 1 



Fig. 


2 . 


Under similar conditions, that is, if the bodies are very 
small compared with the distance between them, two bodies 
are said each to have unit charges if, when unit distance 
apart in air, they attract or repel one another with unit force. 2 

The Electric Field —The attractions and repulsions 


1 Assuming the size of two charged bodies Q and Q, 1 to be very small 
compared with the distance r between them, then the force between 


them E = 5 Q1 


W2 


2 If two small bodies A and 13 have each a charge of one unit of 
positive electricity and are one unit of distance apart, there is one unit 



















ELECTRIC PHENOMENA. 


o 


caused by electrically charged bodies are due to strains in 
the medium separating the bodies. This medium must be 
a dielectric, and the seat of these strains is called the 
electric field. 

Electric Intensity .—The electric intensity at any point 



in an electric field is the force that would be exerted at that 
point on a body charged with a positive unit of electricity. 1 

of force repelling the bodies from, each other. If each had been 
charged with six units of electricity separated by two units of space 

the force of repulsion would have been —— 9 units. 

1 If E be the electric intensity at a distance r from 

(1) A charged point Q. 



(2) An electrified cylinder with charge Q per unit length 

P = 2 3 JI 

r 

(3) An infinite electrified plane surface with charge Q per unit of area 

F = 2 7T Q . 





















6 


RADIO-TELEGRAPHY. 


Lines of Force .—A line of force is a curve drawn in the 
electric field so that the direction of the curve is the same as 
that of the electric intensity at that point. Figs. 2 and 8 
represent approximately the lines of force between two 
equally charged bodies when the bodies are oppositely 
charged, and when they are similarly charged. Fig. 4 
represents the lines of force between the plates of a charged 
condenser. 1 It is to be noted that the direction of the lines 



at the surface of a conductor is always perpendicular to it; 
also the strain is tensile along the lines and compressive at 
right angles to the lines. It is these tensions and pressures 
in the medium that cause the attractions and repulsions of 
electrified bodies and electric charges, but, so long as every¬ 
thing is at rest, the tensile and compressive strains balance 
each other at any point. 

Tubes of Force .—If on any charged conductor a curve be 
drawn enclosing one unit of electricity, and from every point 
of this curve lines of force are drawn till they reach another 

1 See p. 9. 

































ELECTRIC PHENOMENA. 


conductor, the volume bounded by the two surfaces and the 
lines of force is called a tube of force. Lines and tubes of 
force are only representations of the strains in a similar way 
to the pictorial representations of forces in ordinary statics 
by lines. If a plane be drawn at right angles to the direction 
of the electric intensity at any point, then the number of 
tubes that cut unit area is a measure of the electric 
intensity. The expression tube of force gives the idea 
that the forces exist throughout space. In figures it is more 
convenient to show only the lines. The nearness of the 
lines together gives a measure of the number of the tubes of 
force. In the case of a stationary field of force these tubes 
always end on the surface of separate conductors—one 
positive and the other negative. 

Potential .—The tubes of force start from a body more 
positively charged than the body at which they finish. The 
body more positively charged is said to be at a higher 
potential than the other. Travelling in a straight line 
from the body at higher potential to that at lower potential, 
the electric intensity at any point in a given direction 
measures the rate of diminution of potential in that direc¬ 
tion at that point. The lines and tubes of force are always 
perpendicular to surfaces of equal potential; and, travelling 
along a surface of equal potential, the electric intensity at 
right angles to the surface is always the same. The potential 
of a body at rest is also a measure of its power to do work ; 
it can be defined as follows :—If a small body charged with 
a unit of electricity be moved from one position to another 


8 


BADIO-TELEGRAPHY. 


under the influence of other electrified bodies, the electric 
potential 1 at the second position exceeds that at the first 
position by the amount of work done on the body against 
the influence of the other electrified bodies. Potential is 
not work; it is the potential multiplied by the charge that 
is a measure of the total work. If on the whole this small 
body has been repelled by the other bodies, work has been 
done, and the amount of work done is a measure of the 
increase of potential. On the other hand, if the small body 
has been attracted it will have done work and the potential 
will be lowered. 

Perhaps the simplest way to understand potential is by 
considering the potential energy of a swinging pendulum. 
At the end of each half swing the bob is momentarily at 
rest, and the whole of the energy is potential or energy of 
position. 2 Attraction due to the earth pulls the bob of 
the pendulum down ; a small portion of the energy is con¬ 
verted by friction into heat, but the greater portion is 
converted into energy of motion in the pendulum, causing 
the bob to pass the lowest position and swing to a position 
not quite so high on the other side, when once more the 
energy of the pendulum is only potential. But owing to 
the transference to heat energy the bob will be rather closer 
to the earth. And at the end of each half swing the bob 

1 In practice differences of potential are measured in units called 
volts. 

2 The energy is the mass multiplied by its height from its lowest 
position. In this analogy distance from the earth compares witli 
electric potential and mass with electric charge. 


ELECTRIC PHENOMENA. 


9 


will get nearer, till eventually the pendulum comes to 
rest, when the whole of the energy will have become 
heat. 

Another way is to consider the force at any point. This is 
always numerically equal to the rate of variation of the 
potential, but the force and variation of potential act in 
opposite directions. 1 

The potential of a conductor is the potential of the field 
at the surface of the conductor. For practical purposes the 
potential of the earth can usually be taken as zero. 

Capacity .—The capacity 2 of a conductor is the quantity 
of electricity necessary to raise it one unit of potential. 
The capacity of a conductor far away from all other con¬ 
ductors depends solely on its size and shape. When it is 
brought near to another oppositely charged body the electric 
strains cause a redistribution of the charge, making the 
capacity greater. 

Condensers .—When two opposite charged conductors are 
brought very close together, the cajiacity of each conductor 
is increased enormously, and the combination is called a 

1 The electric intensity E in any direction s is equal to the rate of 
diminution of potential U in that direction 

d U 

1 ? _ _ _ 

d s 

At a distance r from a charged point Q 



2 In practice capacities are generally measured in units called 
microfarads. The capacity K of a sphere of radius a, if distant from 
other bodies, is given by 


Iv = a. 


10 


RADIO-TELEGRAPHY. 


condenser. 1 The capacity of a condenser depends on the 
insulating, or rather dielectric, material between the con¬ 
ductors ; accordingly insulating materials are said to have 
different specific inductive capacities. The specific inductive 
capacity of glass, for instance, is about seven times that of 
air. Consider the case of two similar parallel plate con¬ 
densers, one with the plates separated air, the other by 
glass, then if they are charged so that the difference of 

potential is the same in the 
two cases, the glass con¬ 
denser will have a charge 
of electricity seven times 
as great as the air con¬ 
denser, and it will have 
taken seven times the 
amount of energy to raise 
it to that potential. 

The difference between 
insulator and dielectric may 
now be better understood. Both the air and the glass isolate 
the charges of electricity of a condenser from each other. 
The air is found to isolate the charges more completely, so 
it is the better insulator. On the other hand, with glass 
between the charged bodies, it is possible to store a larger 

1 When two parallel plates each of considerable area A are placed a 
short distance r. apart with material of specific inductive capacity k 
between the plates 















































































































ELECTRIC PHENOMENA. 


11 


amount of electric energy, showing that glass is the better 
dielectric. 

The most common form of condenser is the Leyden jar. 
A battery of six Leyden jars, as used by Marconi in short 
distance radio-telegraph stations, is shown in Fig. 5. 
These jars are made of specially prepared glass, coated 
inside and outside with tin foil. The outside coatings rest 
on a sheet of tin foil at the bottom of the tray, which is 
connected to the terminal at the top of the tray to the left. 
Good contact is made to the inside by the cage-shaped 
springs. All the upper terminals are connected together so 
that the electrical effect is the same as having one large jar 
six times the size of the unit. 1 The glass between the two 
coatings acts both as an insulator and dielectric. 

Electric Displacement .—When two electric charged bodies 
act on each other there is a polarization or displacement of 
electricity from the positive body towards the negative body, 
and over any given surface this is measured by the excess of 
the number of tubes leaving the surface over the number 
entering it. The displacement normal to a closed circuit 
is a measure of the charge within the circuit, and is directly 
proportional both to the electric intensity and the specific 
inductive capacity of the medium. 

1 Other forms of condenser are shown in Figs. 135, 155. 

If capacities lc x G etc. be joined in parallel the resultant capacity 

K = 1c i ~f" tc% —|— lc$ etc. 

If capacities k\ h 2 etc. be joined in series the reciprocal of the 
resultant capacity 

1 = i + t + I e t c 

K - h + h + k. 


12 


RADIO-TELEGRAPHY. 


Consider a closed surface shown in section by ABC, 
Fig. G, with no electrified body inside ; the same number 
of tubes enter and leave the surface and there is no 
electric displacement. On the other hand, if there is, say, a 
positively electrified body within the surface (Fig. 7) then 
an excess number of tubes leave the surface, and this 
excess is a measure of the total displacement. In the 
figure only one tube is shown for simplicity. 

Magnetism. — A special 
form of oxide of iron has 
the power of attracting iron 
filings; this oxide of iron is 
said to be magnetic. If a 
piece of steel be stroked 
with this magnetic oxide it 
permanently acquires the 
same properties of attract¬ 
ing iron, and is called a magnet. It will be found 
that a magnet will attract one end and repel the other 
end of a second magnet. If a magnet be suspended in 
the centre it will point in a direction north and south; 
the end which points north is called the north pole, 1 the 
other the south pole of the magnet. The north pole 
of a magnet attracts south poles and repels north poles, 
and generally the behaviour of magnets on each other 
and on iron are very similar to those of electric charged 

1 As the north pole of the earth attracts the north pole of a magnet 
the naming is not systematic. 



Fig. 6. 



ELECTRIC PHENOMENA. 


13 

bodies on other charged bodies. A unit charge of magnetism, 
magnetic intensity, magnetic field, magnetic lines of force, 
magnetic tubes of force, and magnetic displacement may 
be defined in similar terms to their electric analogues. 

Magnetic Displacement, or Induction .—Just as electric 
displacement is proportional to the electric force and the 
capacity of the medium for supporting electric displacement, 
so the magnetic induction is proportional to the magnetic 
force, and the permeability, or capacity of the medium, 
for supporting magnetic induction. 

But, whereas in the electric analogy 
all dielectrics have different capaci¬ 
ties for supporting electric displace¬ 
ment, in the case of magnetic 
induction most substances have 
nearly the same capacity for sup¬ 
porting magnetic induction. Iron 1 is the substance that 
most greatly differs from others, and the permeability of 
iron differs with every sample. 

Polarisation .—Considering the forces of matter on matter it 
is only necessary to think of the existence of matter in space, 
but the habit of thought with which one has to approach 
the understanding of electric and magnetic phenomena is 
different; it is necessary to remember that for every unit of 
positive electricity produced there is a unit of negative 

1 Most substances have the same permeability. Nickel and cobalt, 
however, are further exceptions, as also are the newly discovered 
alloys of copper manganese and aluminium. 



li 


EADIO-TELEGRAPHY. 


electricity ; and for every unit north magnetic pole there is 
a unit south magnetic pole, that is, the matter has become 
polarised. Considering the actions of material bodies on 
each other we have only to think of the actual force of 
gravitation between the bodies, hut in the electric and 
magnetic analogues there is always the polar action causing 
not only attractions and repulsions but rotary forces tending 
to cause electrified or magnetic bodies to set themselves in 
a particular direction. 

The term polarisation is also sometimes used to mean 
the same as displacement. 

Electro-Statics and Electro-Magnetics. — The foregoing 
explanatory remarks have dealt with electric bodies, electric 
fields, and magnets at rest. In radio-telegraphy and most 
other practical applications of electricity and magnetism 
continuous changes are taking place in the electric and 
magnetic fields. During the time these changes take place 
in any electric field a magnetic field is produced and in the 
same way a change of magnetic field gives rise to an electric 
field ; under these circumstances the phenomena are called 
electro-magnetic. 

Electric Currents .—Suppose two bodies to be gradually 
charged by some means. To commence with, there are no 
tubes of force and no displacement. As the two bodies are 
being charged there will be a growing field of electric force 
and electric displacement. The rate of variation of the 
displacement with the time is called the displacement 
current. When there is no alteration in the number of 


ELECTRIC PHENOMENA. 


15 


tubes of force this current ceases, and when the number of 
tubes of force diminish there is a current in the opposite 
direction. 

Suppose the bodies to be charged from some source by 
conductors to points near an air-gap ; a portion of the charge 
will be quickly given up to adjacent parts of each con¬ 
ductor. The charge travelling over the conductor is called 
a conduction current. At any point the total electric 
current 1 is made up of two parts : a displacement current 
and a conduction current. Consider a condenser, consisting 
of two plates separated by air, being charged at its centres; 
there is a practically uniform electric field produced between 
the two plates, and the displacement from the positive plate 
will spread equally over the whole surface, and the total 
displacement current leaving the surface will be uniform. 
At the same time, a portion of the charge spreads from the 
centre to the rim of the plate, leaving some of the charge 
at each point, so that travelling from the centre to the rim 
the charge in motion or conduction current becomes 
less and less, till at the rim it is nothing. 

The following properties of electric currents are to be 
noted:— 

(1) The current always flows in a closed circuit. When 
the circuit A B C, in Fig. 8, is completed, chemical actions 
in the battery B cause a conduction current to flow along 
the wire and a displacement current from the condenser 
plate, C to A. This action goes on until the condenser C xl 


1 Currents are measured in units called amperes. 


16 


RADIO-TELEGRAPHY. 


is charged, that is, till the potential difference between the 
condenser plates is the same as that at the terminals of the 
battery. If, however, the whole circuit were conducting the 
current would persist until the battery were exhausted. 



(2) At any instant of time the algebraical sum of the 
currents taken in all directions at any given point is zero. 
Along a single conductor this is equivalent to saying the 

current leaving and entering a 
surface is the same. 

(3) Every element of current 
is associated with a magnetic 
field. 

(4) When there is a displace¬ 
ment current only, the magnetic 

force is at right angles to the displacement and to the 
direction at which the tubes of force are travelling. In 
Eig. 9, 0 B represents the direction of the electric field 
increasing in the direction 0 A. 0 B is at right angles 
to 0 A and also represents the direction of the displacement 













ELECTRIC PHENOMENA. 


17 


current. The magnetic force 0 C is at right angles to both 
0 A and 0 B. 

(5) When there is a steady conduction current there is 
no displacement, and the magnetic force is at right angles 
to the direction of the current, and also to normals from 
the conductor. In Fig. 10, A 0 represents a short length 
of a conductor carrying a conduction current and one line 



of magnetic force embracing it. In Fig. 11 the conductor 
is shown in section with the magnetic field. 

(6) When there is an alteration in a conduction current 
there is always a displacement current practically normal to 
the surface of the conductor, thus the magnetic force at 
any point is at right angles to both displacement and con¬ 
duction currents. 

Production of Electric Currents .—There are numerous 
ways of producing electric currents; two of these methods 
are more especially utilised, one using chemical reactions, 


R.T. 


c 










18 


RADIO-TELEGRAPHY. 


which we will here only name, and the other the changing 
of the magnetic field through a conducting circuit. In any 
closed circuit, ABC, Fig. 1*2, an increase in the number of 
magnetic lines in the direction D causes a current to How 
clockwise round the circuit, whilst a decrease in the same 
direction or an increase of field in the opposite direction 
would cause a current to flow contra-clockwise. With a 



steady magnetic field (Fig 18), to produce currents in a coil of 

wire, it is thus only necessary to rotate 
the coil so that it cuts the lines of force. 

Resistance and Penetration of Currents 
in Conductors. —Taking the plate con¬ 
denser and considering only the con¬ 
duction current it is found that this 
commences as the tubes of force reach the conductor, but 
it takes a further interval of time for the current to attain 
its maximum value. During this process it penetrates into 
the conductor. This penetration is due to what is known 
as electric resistance, 1 for if the conductivity were infinite 
there would be no necessity for the current to penetrate. 
No substance is a perfect conductor, so there is always a 
penetration of the electric field, and the current, if kept on 
sufficiently long, will flow uniformly through the conductor. 
Electric inertia, 2 however, is always associated with every 
circuit, and this tends to decrease the speed of penetration. 

Uniform Conduction Current. —To produce a steady direct 


1 The practical unit of resistance is called the ohm. 

2 See p. 20. 
























ELECTRIC PHENOMENA. 


19 


conduction current there must be a steady and constant 
difference of electric potential. This difference of potential 
must be maintained by a continuous supply of energy from 
some source, which originally may be chemical, thermal, 
mechanical, or electrical. Tubes of force are streaming 
from this source of electric energy, and the energy 
associated with these tubes, as they penetrate the conductor, 
is transformed into heat. The greater the resistance of the 
conductor, the larger the 
difference of potential re¬ 
quired to keep the current 
uniform. With any increase 
of difference of potential at 
the source more tubes 
stream out, causing first a 

small displacement current; 

. Eig. 13. 

and then, if the increased 

difference of potential be maintained, an increased steady 
conduction current proportional to the increased difference 
of potential. 1 

Electro-motive Force may he defined as the measure of the 
tendency to produce an electric current. For brevity it is 
usually written E. M. F. It is numerically equal to differ¬ 
ence of potential. The one, however, only denotes the 
difference of potential between any two points of a closed 

1 With a steady current C through a resistance r the potential 
difference \ required to maintain the current is given by 

V = Or. 





















20 


RADIO-TELEGRAPHY. 


circuit, whilst the other is the difference of potential at the 
terminals of the source of power when no current is passing. 
When a current flows, the potential difference at the 
terminals diminishes, due to electric losses in the source of 
power, and is no longer a measure of the whole E. M. F. in 
the circuit. E. M. F. must in no case be confused with 
mechanical force. The latter tends to move matter, the 
former electricity. 

Electric Inertia or Self-Induction .—The self-induction 1 of 
a conductor is defined as the number of tubes of magnetic 
induction surrounding the circuit for every unit current 
flowing through the conductor. It is this magnetic field, 
which is always associated with electric currents, that gives 
electric inertia, and this inertia is proportional to the 
current and the self-induction. In the case of a conductor 
it depends on the shape of the conductor and the magnetic 
permeability of the conductor and medium surrounding it. 
A closely-wound helix has large self-induction, as nearly all 
tubes of force round one turn embrace all the other turns. 
Two wires very close together, carrying currents in opposite 
directions, have small self-induction as the magnetic fields 
of each tend to annul one another. Iron compounds, as 
conductors, or in the medium surrounding them, increase 
self-induction enormously. Most other materials act nearly 
equally. 

Mutual Induction — When a second conductor is surrounded 

1 The practical unit used in measuring self-induction is called the 
millihenry. 


ELECTEIC PHENOMENA. 


21 


by tubes of magnetic induction caused by a current in the 
first conductor, then the number of tubes which surround 
the second conductor, due to unit current in the first con¬ 
ductor, is called the mutual induction of the two conductors. 

» 

When two conductors, A and B, carrying currents in the 
same direction, are brought closer together, the magnetic 
lines of force will embrace both conductors, increasing the 
mutual induction and the electric inertia of the system. With 
currents flowing in opposite directions the two fields tend 
to cancel each other, reducing the inertia of the system, and 



the mutual induction is less than for the single circuit. In 
Fig. 14, the conductor B, shown in section, carries twice 
the current flowing in A. Now, when the currents are in 
the same direction (1), the field at F is the sum of the fields 
due to the currents, but if the currents flow in opposite direc¬ 
tions (2) the field at F is the difference of the two. The 
mutual induction of arrangement (1) is three times that of 
arrangement (2). 

Relation between Electricity and Magnetism. It has been 
pointed out that an electric current is always associated with 
a magnetic field. Adding up all the elements of magnetic 
force along any closed circuit, the result is a measure of the 



99 


EA DIO-TELEGE APHY. 


electric current through that circuit. 1 An electric force 
produces an electric current made up of two parts, one 
displacement storing energy in dielectrics, the other a 
conduction current transforming the electric energy into 
heat energy, nnd in certain cases into mechanical energy. 
A magnetic force produces a magnetic current, called 
induction, storing energy, but there is no known magnetic 
conductor, and therefore no magnetic conduction current. 

Energy .— The energy of a body is its capability of doing 
work. A large number of engineering enterprises resolve 
themselves into this problem :—Given a source of energy, 
coal, oil, gas, water-power or chemicals, work is required to 
be done elsewhere. In recent years it has been found that 
often the most convenient and economical method is to con¬ 
vert the energy into electrical energy, lead it to the place 
required by means of conductors, and then convert it again 
into the form of energy required. For instance, it may be 
converted into light, as in the case of electric-lighting; 
heat for electric-cooking; sound through telephones, and 
mechanical energy for driving machinery, tramways, tele¬ 
graphs and bells. The problem in radio-telegraphy is to 
transmit the energy into space and transform it into sound 
or mechanical energy elsewhere without the use of con¬ 
ductors between the two places. 

We have to deal with three different forms of electric 
energy. (1) At any point there is. electric storage of energy 
which is proportional to the electric force and displacement 
1 This is provided there is no permanent mag-net in the circuit. 


ELECTRIC PHENOMENA. 


2 ;i 

at that point ; (2) There is a total magnetic storage of 
energy due to an electric current which is proportional to 
the self-induction of the circuit and the square of the 
current; and (3) There is a transformation of electric 
energy to heat energy whenever there is a conduction 
current, due to the electric resistance ; and the heat energy 
produced is proportional to the current and the electric force. 
The simplest case of the first form of storage is that of a 
Leyden jar, where the total energy stored is proportional to 
the charges and the difference of potential between the two 
coatings. The electric form of storage is the one that 
takes place first in the case we are especially dealing with, 
and one of the principal aims at a transmitting wireless 
telegraph station is to store as large a quantity of electrical 
energy as possible before a disruptive discharge takes 
place. 

Units .—Using electric charges at rest it is possible to work 
out a complete system of units. Starting with two charged 
bodies, they are said to have unit charges when, if separated 
by unit distance (one centimetre), they are repelled from 
each other with unit force (one dyne). In the same way, 
starting with the magnetic properties of bodies, we may 
define unit poles to be such that when separated unit 
distance they will repel each other with unit force. It 
has been pointed out that there is a cross connexion 
between electricity and magnetism; so if we start, say, with 
the magnetic system of units, we can deduce an electric 
system. Doing this, it will be found that the unit of electric 


24 


RADIO-TELEGRAPHY. 


charge is 30,000,000,000 times smaller than the unit defined 
by the magnetic method. The system using electric charges 
is known as the electro-static system of units. The other is 
the electro-magnetic system, and this is used for all practical 
purposes, or rather convenient multiples of these units. 

Dimensions of Electric Quantities .—Most things in nature, 
such as forces, velocities, energy, can be defined in relation 
to the dimensions, mass, length and time. From both the 
electro-static and electro-magnetic systems of units it would 
appear that electric and magnetic properties could thus be 
defined, but this is not the case. The reason why the two 
systems are not the same is due to the fact that in defining 
the electric charges it was assumed that the specific induc¬ 
tive capacity of the medium ( i.e . air) between the charges 
had no dimensions. In the same way, defining the magnetic 
poles, the dimensions of the permeability of the medium 
between them was neglected. The dimensions of these two 
properties are not known, but on them depends the velocity of 
the electric and magnetic field of force to be hereafter con¬ 
sidered. 


CHAPTEE II. 


ELECTRIC VIBRATIONS. 

T ibrations .—The term vibration is used to denote any 
periodic change in a body. A change is called periodic 
when the conditions, after continuously altering, arrive at 
a similar state after a given interval of time. The best 
known and simplest vibration 
is that of the pendulum of a 
clock. The seconds pendulum 
is in the same position and 
moving in the same direction 
every two seconds. The time 
taken for a complete swing to 
and fro is called the period: the 
number of complete swings in a 
second is called the frequency (that of the clock is one half 
per second), and the distance the pendulum swings from its 
perpendicular position is called the amplitude. In the case 
of the clock there is a source of power, a coiled spring or a 
falling weight, to keep the pendulum vibrating. In Fig. 15 
the distance A B is the amplitude of the swing. The time 
taken for the pendulum to move from A to B is quarter of 
a period. 


B 

\ 





Pig. 15. 



26 


RADIO-TELEGRAPHY. 


Damping .—Suppose this source of power to be removed, 
the amplitude of the vibrations would gradually get less, 
due to friction; and the vibrations are said to be damped. 
It is found in such a case, and in most kinds of vibration, 
that the ratio of the amplitude of each swing to the next 



Fig. 16. 

half swing is a constant. Figs. 16 and 17 show the 
relationship between amplitude of vibration and time in 
the case of undamped and damped vibrations. In the case 
of the pendulum swinging with energy being constantly 



supplied, as in the case of a clock, the vibrations can be 
represented by the curve in Fig. 16. The pendulum start¬ 
ing from B (Fig. 15), successive distances from the vertical 
are shown by the curve; the time when it crosses the 
vertical is thus represented by the curve crossing the axis 
OX. Fig. 17 represents a short pendulum vibrating in a 





ELECTRIC VIBRATIONS. 


27 

liquid with no energy supplied, when only four-and-a-half 
complete swings take place before it comes to rest. 

Nodes, Antinodes and Harmonies .—If a loim elastic string 

o o 

be set in vibration by means of impulses at one end it can 
be made to vibrate as a whole, if the impulses follow each 
other in certain fixed intervals of time, depending on the 
mass, length, and tension of the spring. Fig. 18 illustrates 



a string fixed at two points, A and B, made to vibrate as a 
whole. The full thick line shows the position of the string 
at greatest amplitude. After a quarter of a period the 
string is in the position it will assume at rest shown by the 
thin line; in another quarter 

period the string is in the ^ -® 

position indicated by the 20, 

dotted line. A and B are nodes of motion, C is the 
antinode. With a rather quicker motion the string is 
merely agitated, as shown in Fig. 19. If the impulses 
are given at a certain still quicker rate the two halves 
of the string will vibrate as if it were fixed in the centre. 
With a still more frequent rate of impulse the string will 
vibrate as if it were divided into three, as shown in Fig. 20, 
and so on. The positions of the string which do not 
vibrate are called nodes, and the positions where the 










28 


RADIO-TELEGRAPRY. 


amplitude of vibration is greatest are called antinodes; 
thus in Fig. 20 there are four nodes and three antinodes. 
Vibrations are usually not simple but compounded; 
generally there is one principal vibration of much greater 
amplitude than the others. The smaller vibrations, which 
are usually quicker, and therefore have a greater number 
of nodes than the principal vibration, are called harmonics, 
and the principal vibration is then called the fundamental 
vibration. As an example in harmonics, the lowest C of 
a piano vibrates to and fro thirty-three times a second. 
The frequency of the next higher C an octave above is 
twice this amount, and this C is called the second harmonic 
of the lower C. The third harmonic is the G above this, 
which vibrates three times as fast as the fundamental. 

Energy of Vibrations .—As the pendulum or the string 
vibrates it is for a moment stationary at the maximum 
distance from the normal, before it changes its direction 
of motion. The energy for the moment is all potential or 
energy of position. As the pendulum and string pass the 
normal position in which they would naturally rest they 
have no potential energy. Some has been wasted as heat or 
radiated into space ; the remainder has all been transformed 
into kinetic energy or energy of motion. In intermediate 
positions the energy is partly potential and partly kinetic. 

Interference. Syntony .—If the impulses are given to the 
string too quickly or too slowly it will not vibrate with 
fixed nodes, but the disturbances will tend to destroy one 
another, and there will be spasmodic ripples along the 


ELECTRIC VIBRATIONS. 


29 


string. This is due to the lateral forces acting in opposite 
directions when the disturbance is reflected back from the 
end, and is called interference. When the impulses follow 
each other so as to make the string vibrate with definite 
nodes, the vibrations are said to he syntonic. If syntonic 
impulses are given to a vibrating string just sufficiently 
strong to balance the damping, the amplitude of vibration 
will remain the same. With stronger impulses the 
amplitude of the vibrations will increase. 



Fig. 21, 


Fig. 22. 


Phase .—At any point and time when two vibrations of 
the same periodicity are exactly in the same relative state 
and altering in the same direction, they are said to he in 
phase; otherwise they are out of phase. Consider two 
vibrations, A and B, the maximum amplitude of A being 
twice that of B. In Fig. 21 the vibrations are shown in 
phase, and C is the compounded vibration ; in Fig. 22 A is 
quarter of a period in advance of B, whilst in Fig. 23, A is 
half a period in advance of B. The magnitude of the 
resulting vibration is shown by C, and it will be noticed 




RADIO-TELEGRAPHY. 


that if in the third case the individual vibrations had been 
equal they would have exactly cancelled each other. 

Mass and Compliancy oj Vibrating String .— It should be 
here pointed out that the nature of the vibrations depend 
on the density and tension. The greater the mass and the 
smaller the tension the longer the period and the smaller 
the frequency. The mass gives inertia to the system. 
The greater the mass the less is the amplitude of vibration 
for a given impulse. The density also gives inertia to the 


string. The tension gives 
spring. The more the ten¬ 
sion the stiffer the spring. 
The opposite of stiffness is 
compliance. The greater the 
compliance the larger the 



A 


Fig. 23. 


amplitude of vibration for a given impulse. It is thus seen 
that inertia and compliance impart opposite properties to the 
vibrating string if we consider the amplitude of vibration, 
but the period of vibration is altered in a similar manner by 
each. If an impulse be given to a long, very light string, 
held loosely so that the density and tension are both smalh 
the amplitude of the first vibration is large, but it rapidly 
dies away. If the string is made more massive the first 
amplitude will be much less owing to the increased inertia, 
but the momentum imparted will be greater, so the vibration 
will be less damped. These vibrations can best be studied 
by vertically suspending a long india-rubber cord, and 
giving the necessary impulses at the bottom end. 




ELECTRIC VIBRATIONS. 


31 

Electric Vibrations ^—If two coatings of a condenser be 
charged, one with positive electricity and consequently the 
other with negative electricity, and if a small air-gap be 
placed in the conducting wire between the two coatings, when 
the difference of potential is sufficiently great, a disruptive 
discharge will take place across the gap. Feddersen, by 
observing the reflection of the spark in a rapidly rotating 
mirror, was able to show that, 
under certain circumstances, after 
the first discharge from the posi¬ 
tive coating there was a weaker 
spark in the opposite direction, 
proving that the electric charges 
on the condenser coating had be¬ 
come reversed. Under suitable 
conditions this reversal may take 
place a large number of times 
before the jar is discharged com¬ 
pletely. This phenomenon is 
called an electric vibration or oscillation. Just as the 
nature of the vibrations of a string depend on the mass, 
compliance and friction, Lord Kelvin has shown that 
the vibrations in an electric circuit depend on the self- 
induction, the capacity and the resistance of the circuit. 
Also in the electric analogue we have charge instead 
of position, and electric current takes the place of motion. 
Just before the spark the whole of the energy is potential, 
but after a quarter of a vibration the potential energy 



















32 


RADIO-TELEGRAPHY. 


has vanished, and so have the charges of the condenser; 
the energy of the circuit is now kinetic and due to the 
electric current. A quarter of a period later all the energy 
of the circuit is again potential, but with positive and 
negative charges in reversed positions. In Fig. *24 (a) 
depicts an oscillator. When this is fully charged 1 just at 
the moment of sparking there is no current, and the distri- 

i 

bution of potential is shown at {b). A quarter of a period 
later the energy is all kinetic, and the ordinates (c) measure 
the relative currents along the oscillator. It will be seen that 
there are nodes at A and B, and at C is an antinode of 
current. At the end of half a period the energy is all poten¬ 
tial and distributed as shown at (d), showing C to be the posi¬ 
tion of a node with A and B antinodes of potential. Again, 
after another quarter period the distribution is kinetic, the 
maximum current being somewhat smaller, bowing in the 
opposite direction, and so on. During the oscillations the 
current at the two distant ends is always zero, and in the same 
way the potential somewhere near the middle of the spark gap 
remains constant. Also when the current curve is as shown 
at (c), the potential curve is a straight line through the axis of 
the oscillator, and in the same way when the potential curve 
is as shown at (d), the current is zero along the whole length. 
The period of vibration depends solely on the product of the 
self-induction and the capacity. With a given supply of 
energy, the amplitude of vibration is diminished by self- 
induction, and increased by capacity in the circuit, but as in 
1 How tlie oscillator is charged is explained later. 


ELECTRIC VIBRATIONS. 


33 


the case of the vibrating string the electric inertia gives 
momentum, and forces the waves on. Kirchhoff was the first 
to realise this action in 1858, but its complete significance 
was not understood till Oliver Heaviside showed the help 
self-induction gave to long-distance telephony. Heaviside 
also considers that self-induction may actually represent the 
inertia and inductance represent momentum. We may 
thus compare the electric vibrations with the mechanical 
vibrations. Thus :— 


Electric. 

Permeability. 

Capacity. 

Resistance. 

Current. 

Charge. 

Self-induction. 

Inductance. 

Potential. 


Mechanical. 

Density. 

Compliancy. 1 
Frictional resistance. 
Velocity. 

Amplitude of displacement. 
Mass. 

Momentum. 

Position. 


The characteristics of electric vibrations may be sum¬ 
marised as follows :— 

(1) To produce a primary electric vibration with spark 
telegraphy, it is usual to have opposite charges of electricity 
separated by a gap of air or other dielectric. 

(2) These charges must be sufficiently close together, that 
is, the gap must be sufficiently small for the strain between 

1 Compliancy is the opposite of elasticity, and is the absence of 
power to return to its original state after the removal of applied forces. 


R.T. 


D 


34 


RADIO-TELEGRAPHY. 


the charges to become large enough to cause a disruptive 
breakdown of the gap.' 

(3) The resistance of the circuit 1 must he small. 

(4) Before the discharge the energy is potential. 

(5) During the discharge a spark passes across the gap, 
a current Rows, and the energy changes to kinetic till the 
moment the system is completely discharged, when the 
energy is all kinetic and the current is a maximum. 

(6) When the system is completely discharged the current 
still persists, gradually getting less and charging the system 
in the opposite way till the energy is once more all potential. 
The strain is sufficient to again break down the air-gap and 
the operation is repeated. 

(7) When the system is again charged as at first, a com¬ 
plete vibration has taken place. The number of complete 
vibrations per second is called the frequency, and the time 
of a complete vibration is called the period. 

(8) The total charges stored at the end of each half swing 
are less than at the previous half swing, and also the total 
current during each half swing is less, but the ratio of the 
amplitude of both the charge and the current of each swing 
to the next is the same. This is called the damping of 
the oscillations. 

(9) This damping in the case of a condenser circuit is due 
to the resistance of the circuit and consequent loss of energy 

1 The resistance of tlie oscillating circuit should be infinite before 
the first disruptive discharge, and as small as possible whilst the 
oscillations last, becoming infinite again when the vibrations cease. 


ELECTRIC VIBRATIONS. 


35 


through heating. Above a certain resistance in any circuit 
the system is completely discharged in the first half swing, 
and no true vibration takes place. With the vibrators used 
in wireless telegraphy the resistance of the circuit or circuits 
can be made very small, and it will be seen later that in 
aerial circuits most of the damping is due to radiation of 
energy. 

(10) The time taken for a complete vibration depends on 
the capacity, self-induction and resistance; but, if the resis¬ 
tance be sufficiently small to allow vibrations, it may usually 
not be taken into account. 

(11) The effect of capacity is to increase the amplitude of 
charge and current; self-induction diminishes the amplitude 
but increases the momentum. 

(12) The damping varies as the square of the resistance, 
directly as the capacity and inversely as the self-induction. 
It will be shown later, however, that in the case of a 
circuit containing a spark-gap the effect of adding capacity 
is not only to increase the amplitude, but also, by 
decreasing the resistance of the spark-gap, to diminish 
the damping. 

, (18) On the other hand it is often difficult to increase the 
self-induction without increasing the resistance and damping. 
Unfortunately the self-induction cannot be increased by 
placing iron in the magnetic field, as the loss due to changes 
in magnetising iron produces considerable damping 

It may be here noted that another method of producing 
electric vibrations due to Duddell adapted by Poulsen is 

d 2 


86 


RADIO-TELEGRAPHY. 


described elsewhere ; also several methods due to other 
inventors are touched on. 

In the case of electric vibrations produced by a spark, 
Fig. 17 would represent the alterations of current with time, 
say at the antinode of current; and in the same way it 
represents the alterations of potential at the antinodes of 
the oscillator. Poulsen claims to produce vibrations that 
would be in a similar way shown by Fig. 16. 

Oscillation Constant .—The square root of the capacity of 
a circuit multiplied by the square root of the self-induction 
is called the oscillation constant of the circuit. For different 
circuits, as long as the oscillation constants are the same 
the natural periods of vibration are the same, though one 
circuit may have large inductance difficult to set in vibra¬ 
tions of large amplitude, whilst the other may have large 
capacity easily set vibrating but with small inertia to keep 
the vibrations from being damped out. 

Stationary Waves .—The simplest form of vibration of a 
string is when it is fixed at two ends and vibrates as a whole ; 
with a quicker rate of impulse the string will vibrate as if the 
central point were fixed ; quicker still it will vibrate as three 
strings having four nodes, and so on. If there are at least 
five nodes, at any moment there will be two points on the 
string both the same distance from the mean position and 
both moving laterally in the same direction. The distance 
between these two points is called a wave length. In Fig. 20 
A C is the wave-length. It will be seen that the funda¬ 
mental vibration of the string is half a wave-length; for 


ELECTRIC VIBRATIONS. 


37 


the second harmonic the length of the string is a wave¬ 
length ; for the third harmonic it is a wave-length and a 
half, and so on. The fundamental and harmonic dis¬ 
turbances all travel along the string with the same initial 
velocity. This velocity depends solely on the nature of the 
string, but the length of the string and the nature of the 
impulse given determine whether the movement takes the 
form of the fundamental vibration, harmonics, or merely 
disturbances without definite wave length. 

Secondary Electric Vibrations .—If a straight conducting 
wire or a helix be brought into contact with a charged con¬ 
ductor as has already been pointed out, the total charge is dis¬ 
tributed over the two in a period of time depending on the 
self-induction and capacity of the wire or helix, supposing 
the resistance be so small that it need not be taken into 
account. This is analogous to giving a definite steady lateral 
pull to the stretched elastic string. But suppose instead that 
the wire or helix be brought into contact with an electric 
circuit in which oscillations are taking place, the electric 
impulses given to the wire or helix will produce an electric 
vibration in it provided the oscillation constants for the two 
circuits bear a special relation to one another, just as an 
alternating impulse would set up vibrations in a string, pro¬ 
vided the impulses were properly tuned with the natural 
vibration of the string or one of its harmonics. 

Velocity of Moving Charges along Wires .—It will be 
remembered an electric charge on a conductor is always 
associated with an electric field of force. The energy of 


38 


RADIO-TELEGRAPHY. 


the field is outside the conductor, and where this field 
touches another conducting surface a charge is formed. 
Thus on a long wire a charge at one end tends to spread 
over the whole conductor with the speed of light; but the 


^/WVVWVVWA 




B 


Fig. 2 b. 


ill 


AAAAA 


-o o 


AAAAAA 


Fig. 20. 


growing charge or electric current on the wire has the effect of 
tending to cause an electric field of the opposite sense to be 
formed, which has to he continuously wiped out by the 
oncoming energy, so that though the wire throughout its 


AAAAAi 



AWWW 


I 


AAAAAi 


-o o 


AAAAAA 


Fig. 28. 


entire length commences to get charged at the speed of 
light, the time taken for the current to reach a maximum 
is much longer. When the wire is a finite length and 
surgings take place, the commencing current returning 
from the far end of the wire may get wiped out owing to it 
being out of phase with the advance current, and only the 














































ELECTRIC VIBRATIONS. 


39 


giowth of charge that is in phase with the natural period of 
oscillation persists. This gives an apparent velocity of 
propagation which only depends 
on the oscillation constant of 
the circuit. 

Methods of Producing Secon¬ 
dary Vibrations. —There are three 
methods of producing secondary 
vibrations. (1) By actual contact 
of wires. This method is shown in Fig. 25. A is the 
primary circuit with spark gap G, condenser C, and helix 
of wire I. The secondary circuit B is a helix of wire; it 
may, however, be a closed circuit, as in Fig. 2G, contain¬ 
ing a condenser. (2) By electric induction, 


vvvvvvvn 




-o o 


Eig. 29. 




as shown in Figs. 27 and 28; and (B) by 
electro-magnetic induction, as in Figs. 29 
and 30. Diagrams of each method are 
given. Figs. 25, 20, 29 and 30 represent 
typical circuits generally employed to obtain 
secondary vibrations in radio-telegraphy. 

Method of Examining Electric Vibrations 
in Wires. —It is a very simple matter to 
examine these vibrations by means of a 
Geissler tube. 1 If one pole of such a tube be connected 
to different points of an oscillating circuit it will glow 


I 


—O O- 

Fis. 30. 


1 A Geissler tube consists of a glass filled with rarefied gas, and has 
two metal terminals for an electric current to flow from one to the 
other through the gas. The current causes a nebulous glow of light. 


















40 


RADIO-TELEGRAPHY. 


according to the amplitude of potential change at that 
point, showing brightest at an antinode and dark at a 
node. The fundamental electric vibration generally 
is one quarter of a wave-length. Instead of there being 
two nodes, one at each end, as in the case of the 
vibrating string, there is a node of potential at the point 
where the secondary vibrating circuit is attached, and an 
antinode at the free end, and vice versa a node of current 

at the free end, and an antinode of 
current at the fixed point. Also in 
the case of the harmonics, the con¬ 
ditions must be such that there is 
a node at one end and an antinode 
at the other. In Fig. 31 the straight 
wire 1 A 13 is supposed to touch at A 
a vibrating circuit having the same 
oscillation constant; the maximum 
amplitudes of potential are shown 
by the full lines, and the maximum 
amplitudes of current are shown dotted for the principal 
vibration (a) and the first (b) and second (c) harmonics. 

Professor Fleming, in the Cantor lectures delivered in 
1905, gave the results of some experiments on this subject. 
He used a fixed length of helix, and varied the capacity and 
self-induction of the primary vibrating circuit so as to 
produce waves corresponding with the fundamental, first, 

1 A similar set of curves would be obtained by touching an oscillatory 
circuit with a helix of wire. 






ELECTRIC VIBRATIONS. 


41 


second, and third harmonics of the helix. This helix was 210 
centimetres long and consisted of 5,470 turns of wire. The 
detecting Geissler tube contained rarefied neon gas, which 
Professor Fleming found gave the most sensitive results. 
The experiments with each harmonic gave the fundamental 
wave of the helix as 871 centimetres. The rate of propa¬ 
gation of the disturbance along the helix was calculated 
from the measured self-induction and capacity of the 
primary vibrating circuit. From the experimentally found 
wave-length of the fundamental and harmonics an almost 
identical velocity of about 1,200 miles a second was 
obtained. 

The positions of the antinodes of current can be studied 
by breaking the helix at different points and inserting a 
short length of very thin wire, which would get heated 
more or less depending on whether it were inserted at a 
node or antinode. It will be noticed that when there is 
more than one node in an electric vibrator, the current at 
the same moment of time will be flowing in opposite 
directions in the parts of the wire separated by the node. 

In carrying out experiments with secondary vibrations it 
must he remembered that the capacity of the helix will 
vary, depending on its relative position to other bodies, and 
under certain circumstances, though the oscillation con¬ 
stants be the same, there will be an interaction between the 
two circuits causing compound waves in the two circuits. 


CHAPTER III. 


ELECTRO-MAGNETIC WAVES. 

History .—Certain simple electric and magnetic phenomena 
were known to the ancients, but it was not till 1819 that 
Oerstedt, of Copenhagen, demonstrated the interaction 
between a magnet and an electric current. Ampere shortly 
afterwards showed that conductors carrying steady electric 
currents acted on magnets in the same way as if the com¬ 
plete electric circuit were a magnet, and that, moreover, 
the electric circuits acted on each other, attracting and 
repelling in the same way as magnets. These and other 
properties of electricity gave ample scope to the mathema¬ 
ticians of the time, and a complete mathematical theory 
was constructed which took into account all the facts then 
known. Just as all the perturbations of the heavenly bodies 
were being worked out with precision without any con¬ 
sideration of any substance between the bodies, so also were 
the motions and interactions of electrically-charged bodies, 
magnets, and conductors conveying currents. Then came 
Faraday’s conception that the medium between the bodies 
was the seat of the strains and stresses. Using this 
hypothesis Faraday made many brilliant discoveries. 
The most useful and probably the most brilliant was that 


ELECTRO-MAGNETIC WAVES. 


43 


the alteration of the magnetic held through a circuit produced 
an electric current in that circuit, thus laying the founda¬ 
tion for the electric light and tramway industry of to-day. 
It still remained for Faraday’s conceptions to he formulated 
in mathematical shape, and this was not done till 1873, 
when Clerk Maxwell published his treatise on “ Electricity 
and Magnetism.” This work, which the author modestly re¬ 
garded as being principally for the assistance of under¬ 
standing Faraday’s mode of thought, was full of new 
discoveries; but we are chiefly concerned with only one of 
these. Clerk Maxwell formulated the hypothesis that the 
electro-magnetic strains in the medium travelled at a 
definite speed, depending on the permeability and specific 
inductive capacity of the medium. He showed, further, that 
in air this speed was the same as that of light, which led 
him to suppose that light was an electro-magnetic wave 
probably due to electric vibrations taking place over the 
surfaces of masses of molecular dimensions. That electric 
vibrations could he produced in electric circuits had been 
demonstrated by Feddersen in 1857, and the complete laws 
governing the conditions under which these vibrations 
would occur were worked out by Lord Kelvin in 1853. 

At the same time it seemed hopeless to expect any experi¬ 
mental data to strengthen Maxwell’s hypothesis, hut within 
twenty-five years from the publication of Maxwell's treatise 
Heinrich Hertz, a German professor, gave to the world a 
complete demonstration of electro-magnetic waves. Hertz 
was not content to produce these waves; he measured their 


44 


RADIO-TELEGRAPHY. 


length and their frequency. He reflected them by means 
of parabolic mirrors, and he showed that just as there is a 
change of direction in the wave front of light when it 
penetrates a new material, so also are the electro-magnetic 
waves refracted when they pass from one substance to 
another. 

Waves .—In the case of a string vibrating, when fresh 
impulses are not given to it, the amplitude of the oscilla¬ 
tions becomes less and less. This damping is partly due to 
loss by friction, but it is also due to the string imparting 
its vibrational energy to the surrounding air. As the string 
moves laterally outwards from its normal position it pro¬ 
duces a compression of the air in front, and this state of 

compression is imparted from one molecule of air to the 

# 

next. Behind the moving string there is a rarefaction of 
air. When the string moves in the opposite direction the 
conditions are reversed; there is rarefaction where pre¬ 
viously was compression and vice versa. There is thus an 
alternate state of compression and rarefaction of the air whilst 
the vibrations last. The energy of the vibrating string is 
being radiated as waves of compression and rarefaction of 
air into space. In certain special cases, if the string 
is neither vibrating too quickly nor too slowly, a membrane 
of the ear is set in vibration, and we have the sensation 
called sound. Any sensitive membrane having the same 
natural period of vibration as the oscillating string, and 
placed so as to be acted on by the waves of alternately com¬ 
pressed and rarefied air, will also be set in motion. 


ELECTRO-MAGNETIC WAVES. 


45 


Velocity of Propagation—Frequency and Wave-Length .— 
The velocity of propagation of a wave depends on the 
medium through which the wave is moving. The greater 
the elasticity 1 of the medium and the smaller the density 
the greater the velocity. The frequency of the wave is the 
number of times per second that the medium is in the same 
state, and changing in the same way per second. In the 
case of a vibrating string consider the air immediately next 
the string where it is furthest extended (see Fig. 82). As 
the string moves from B 
to A the air is being 
compressed at A. Again, 
as the string moves from 
A to B the air at A is 
becoming rarefied till it 
reaches B, when com¬ 
pression begins again. 

It will be seen that the air at A goes through a complete 
change of state in the same time as the string makes a 
complete vibration, and in general the period and frequency 
of a wave are always the same as that of the vibration 
causing the wave. 

Now this compression travels outwards from the string, 
and at the beginning of a second vibration the air along a 
nearly spherical surface in space at C will be just starting 
to be compressed from the first vibration, and again at the 

3 Elasticity is the power a body has to resume its original shape and 
size after the removal of applied forces. 






46 


RADIO-TELEGRAPIIY. 


beginning of a third vibration a disturbance will have 
started at I). The distance A C is equal to C D, and is 
called the wave-length. It will be seen that the quicker 
the speed of propagation the longer will be the wave-length, 
but the greater the frequency of the vibration, that is, the 
shorter the period of one vibration the shorter will the wave¬ 
length become. It is important to realise that the air does 
not travel from A to C. It is only the density of the air 
that periodically changes. 

Amplitude of Wave Disturbances .—In the special case we 
have been considering the amplitude of the disturbance is 
the greatest difference caused in the density of the air from 
its normal state. After several vibrations, when the string 
is at A position, the air is densest at A, C and D ; rarest at 
A', C', D', etc., and these are points where the disturbance 
has the greatest amplitude. As the string vibrates back to 
B the positions of greatest amplitude shift from C to A, I) 
to C, and C' to A', and the points A, C and D become posi¬ 
tions of greatest rarefaction; that is, as the string vibrates 
between A and B, the initial distance A B depends on 
force exerted and the properties of the string, whilst 
periodical disturbances take place between A and C, C and 
D, etc. 

Suppose that the string is not permanently kept in motion 
and the vibrations are damped, the amplitude of the swing 
and the distance A B becomes gradually less ; the energy of 
the wave at A with its amplitude will also be less at each 
vibration, both dying away together; but the wave-length, 


ELECTRO-MAGNETIC WAVES. 


47 


depending only on the nature of the medium of trans¬ 
mission, remains the same. 

The energy of the vibration extends out in space in all 
directions. At C the amplitude of the disturbance is much 
less than at A, and at a short distance the amplitude of 
disturbance becomes greatly diminished. 

The Vibrating Receiver .—A body having the same natural 
period of oscillation as the vibrating string will be set 
in vibration by the wave. It is not necessary that the 
elasticity nor the mass of the receiver be the same as the 
vibrator, but the quotient of these must be a constant. 

The frequency of vibration will be the same as that of 
the string; the amplitude of vibration will be small at first, 
but, if the friction of the receiver be small, the amplitude 
will gradually increase, as long as the energy received from 
each succeeding wave is greater than the loss in the receiver 
during the period of the preceding wave. 

Electro-magnetic Waves .—Under certain conditions, when 
electric oscillations take place in wires, a part of the energy 
of the oscillation is radiated into space as electro-magnetic 
waves of definite frequency and length depending on the 
oscillation constant of the vibrator. From the theory of 
Maxwell and the experiments of Hertz, the velocity of the 
propagation of the wave is about 186,000 miles a second. 
These waves can be detected by means of a vibrating 
circuit placed in the path of the waves having the 
same oscillation constant as the primary vibrator. To 
understand the elementary properties of these waves it 


48 


RADIO-TELEGRAPHY. 


will be best to briefly describe a few of Hertz’s experi¬ 
ments. 

Hertzs Experiments. —Hertz's apparatus consisted of an 
electric vibrator charged by means of an induction coil and 
a resonator having the same oscillation constant as the 



Eig. 33. 


vibrator. Various modifications of vibrator and resonator 
were used; a typical form of vibrator is shown in 
Fig. 33. 

The vibrator always consisted of two straight conductors 



with small capacities at the extreme ends, the arms being- 
separated by an air-gap. The resonator consisted of a 
loop of wire, and of such a length and shape that the 
natural period of electric vibrations in it was the same as 
the vibrator, and it was broken at one point by a minute 
air-gap. This loop of wire was placed in a central position 











ELECTRO-MAGNETIC WAVES. 


49 


some distance from the oscillator with no walls near by, 
otherwise the reflection from the walls would interfere. 

Experiment I .—Let the resonator be placed as shown in 
Fig. 34, with the air gap at the highest vertical position, as 
shown at C. When sparks take place at A, there is no 
spark at the resonator. Turn the resonator gradually 
round in its own plane ; the resonator will become more and 
more responsive till it has 
been turned a quarter of a 
revolution ; when at D, the L ~~p 
sparking at the resonator_A 



o 


gap is a maximum, becom¬ 
ing less as the resonator is 
turned on, till at E there 
is no response, the sparks 


again increasing till the position F is reached, where the 
results are similar to position D. 

Experiment II .—Starting as in experiment I. with the 
resonator in position D or F, and gradually rotate it about 
its horizontal axis, sparking in the resonator will gradually 
become less and less, till in the position shown in Fig. 35 
there will be no sparking. 

Experiment III .—Starting with the resonator in the 
position shown in Fig. 35, and gradually rotate it in its 
own plane, there will be no sparking at any position. 

Closed Tubes of Electric Force .—The results of these 
experiments are what would be expected from Maxwell's 
theory. A line of force from a linear vibrator when fully 


Ii.T. 


E 









50 


KADIO-TELEGEAPHY. 


charged may be shown roughly as in Fig. 36. A spark 
takes place. If the resistance be sufficiently high, the time 
of discharge is prolonged sufficiently for the whole electric 
field to shrink back, the whole of the energy being dissipated 
in the vibrator, but with a lower resistance, the discharge 
takes place quicker. As the shortest tubes vanish, the 
lateral pressure on the remainder is diminished, and the 
diminution of pressure is greatest near the vibrator. This 

diminution of pressure from the 
inside causes first a flattening 
and then squeezing in of the 
tubes as they are rapidly shrink¬ 
ing inwards. At a certain stage 
the pressure becomes sufficiently 
reduced for the sides to meet and 
two tubes are formed, one shrink¬ 
ing into the vibrator whilst the 
closed tube is radiated into space. 
The shrinkage and breaking up 
of a tube are shown in successive positions 1, 2, 3, 4, 5 in 
the figure. It will be remembered that a tube of force 
merely depicts the electric intensity or the size and direction 
of the electric force. 

In most of the diagrams in this book only the lines of 
force are shown. It will be remembered a line depicts the 
direction of the force and not its size. In general, lines of 
force only are shown in diagrams of the electric field, the 
nearness of the lines to each other representing the strength 










ELECTRO-MAGNETIC WAVES. 


51 


of the field. In some cases it is however best to use the 
word tube, as it gives a better idea of the field filling 
space. 

Travelling along a closed tube the electric force is in one 
direction all round in a similar way as in the case of a 
smoke ring; there is the same force all the way round 
tending to make the smoke travel in a ring, but in the 
smoke ring there is a motion of the smoke ; along the 
electric tube there is no motion. A simple and more 
perfect analogy is found in a closed magnetic tube. A 
conductor carrying a current is always surrounded by 
closed tubes of magnetic force. A small magnet will tend 
to set itself longitudinally along the lines of magnetic force, 
but there will be no tendency for the magnet to move 
along the lines; also a small iron wire placed along 
the tube will become magnetised. In the same way an 
electrified body will tend to set itself longitudinally along 
the lines of electric force, and a conductor placed in the 
field will become oppositely electrified at the two ends. 

There is this remarkable difference between the closed 
magnetic and electric tubes. When the magnetic field is 
due to a steady electric current it is stationary ; but it has 
been found impossible to produce a steady magnetic current, 
so that closed electric tubes are never found at rest. Under 
ordinary conditions, when an electric current ceases, the 
magnetic field shrinks back to nothing. In the same way, 
when magnetic induction ceases, the electric field shrinks 
to nothing, and it is only when there are violent surgings 

e 2 


o2 


RADIO-TELEGRAPHY. 


of electricity that closed magnetic and electric tubes are 
radiated into space. 

Representation of Electro-magnetic Wave striking a Hertz 
Resonator .—An attempt is made in Fig. 37 roughly to 
depict an electric field striking a Hertz resonator. The 
arrow A shows the direction of motion, the velocity being 
186,000 miles a second. The lines of force are shown 
closer together at B and C, because these are positions 



Fig. 37. 


where the field is strongest. The directional character is in¬ 
dicated by arrows, and at 0, halfway between B and C, the 
direction of the field changes sign, i.e. its direction. The 
tube C is shown striking the conductor at F and leaving it 
at E. Asa conductor is the seat of dissipation of energy and 
does not support electric strains, the pressure is lessened in 
the neighbourhood of the resonator, distorting the field. A 
tube of force terminating or leaving a conductor constitutes 
a charge of electricity. As shown, the field is most intense 
at E and F, so the electricity on the resonator is densest at 
these points, positive at E where the force is from the 
























ELECTRO-MAGNETIC WAVES. 


53 


resonator and negative at F. As the field travels, the 
position of densest positive charge travels in the direction 
of the arrow, the moving charge constituting an electric 
current. The distortion of the field, causing it to travel 
slower at the surface of the conductor, depends on the 
capacity and inductance of the resonator circuit. Suppose 
these constants are such that the maximum positive charge 
travels from Gi to G 2 , following the arrow, in the same time 
that the field travels from B to C. If the travelling field 
were now suddenly to cease, there would be a positive 
charge at G 2 and a negative charge at Gi, so a current 
would flow from G 2 to Gi. If the wave, however, persisted 
and remained nearly the same strength, it would also have 
caused an additional current to flow from G 2 to Gi, so that 
the total current might be nearly double that during the 
first half wave. When the charges are greatest at Gi and 
G 2 the energy is potential, and the difference may soon 
become sufficient for a spark to pass. It was this spark 
that enabled Hertz to study these waves. 

If, however, the moving charge travelled from Gi to F 
during the half period, secondary disturbances would be set 
up; the disturbance due to the first half wave still tending 
to send a current from F to G 2 , whilst the on-coming wave 
would be tending to send one from G 2 to F. The vibrations 
would no longer be syntonic, and the difference of potential 
would probably not become sufficiently large for a spark to 
pass. With the gap at G 3 the tendency of the currents is 
to flow from G 3 to H in opposite directions around the 


54 


RADIO-TELEGRAPHY. 


loop, which now may be considered as two resonators with¬ 
out any tendency to spark across the gap. It is also 
obvious that no electric strains can be set up across the gap 
when the plane of the resonator is either turned through a 
right angle round the axis Gi K, wherever the gap may be. 

The Magnetic Field .—Associated with the electric field is 
the magnetic field. In Fig. 87 the absence of lines 
denotes the strength of the field. It is greatest at 0, and 



Fig. 38. 


nothing at B and C. 1 The direction is at right angles to 
the paper, the lines of magnetic force being closed circles 
round the oscillator. 

A Method of Depicting the Electric and Magnetic Fields. 
—Perhaps the simplest way to picture the fields is by 
co-ordinates. In Fig. 88, H represents a Hertz oscillator. 
Let 0 be any point in space some considerable distance 
from H. Draw a line 0 Y in space representing the direc¬ 
tion of motion of the wave. Draw 0 Y parallel to the axis 


1 See footnote, p. 55. 











ELECTRO-MAGNETIC WAVES. 


oo 


of the oscillator and perpendicular to 0 X. The electric 
field at points along 0 X will he greatest in the plane 
0 X Y, and nothing in the plane at right angles to it. 
Draw 0 Z perpendicular to the plane OXY; the magnetic 
force will be greatest in the plane 0 X Z. If 0 X represents 
distance in space the intensity of the field at any instant at 
points along 0 X may be represented by 
a curve A B C D. The distance of the 
curve from 0 X is the intensity of the 
field at that point. In the same way the 
strength of the magnetic field may be 
depicted by the curve E F G K. 1 

At any point M along 0 X the strength 
of the electric field is represented by the 
ordinate M B, and the magnetic field by 
the ordinate M F. 

Representation of a Train of Waves .— 

Fig. 38 represented the intensity of 
the field of electric force along an axis. 

A train of waves is roughly depicted in 
Fig. 39. The lines are the positions of maximum field. 
From B the field shrinks back into the oscillator; C D E 
are points of no field at the instant of time taken. C E is 

1 According to O. C. Ross (“Electrician,” September 20, 1907), 
Fig. 38, would represent the electric and magnetic fields in a conductor 
only ; when a wave has reached a quarter of a wave length from the 
oscillator the electric and magnetic fields are in phase and so continue 
as the wave travels out into space. 






56 


RADIO-TELEGRAPHY. 


the wave-length. The rapidly thinning of the lines shows 
to a small degree the weakening of the field as it travels 
into space. 

The Medium through which Electro-magnetic Waves are Pro¬ 
pagated. —In the case of the vibrating string the energy is 
transferred from one molecule of the string to those next it, 
and with the consequent wave radiated out, the transference 
of energy is from one molecule to the next, of gas, liquid or 
solid, as the case may he. Electric transference of energy 
always takes place through the medium, which both fills inter¬ 
stellar space and the space between the molecules of matter, 
solid, liquid or gaseous. This medium is called aether, and it is 
the medium in which everything is immersed. The electric 
and magnetic fields are the strains in the aether. When the 
energy of the field is potential the strains are electric, when 
it is kinetic the strains are magnetic. The transference of this 
energy is at a speed depending on the elasticity and density of 
the aether, the speed being less when the aether is hound up with 
liquid or solid dielectric. The speed in air or interstellar space 
is about 186,000 miles a second. The action of a conducting 
wire is to guide the field as a water pipe guides the flow of water. 

Comparative Duration of Vibrations .—Suppose the arms 
of a Hertz vibrator be connected to a varying source of 
electricity so arranged that the vibrator is fully charged 
and discharged by sparks two hundred times a second. 
Consider what takes place during each period. To com¬ 
mence with, the two arms of the vibrator are at the same 
potential, and there is no charge. The arms are now 


ELECTRO-MAGNETIC WAVES. 


57 


continuously charged till at one four-hundredth of a second 
the difference of potential is just sufficient to cause a break¬ 
down of the air between the knobs. During the time the 
vibrator was being charged tubes of force were being 
generated, stretching from the positive to the negative 
arm. This action started immediately there was any 
difference of potential, and continued as the difference of 
potential increased. Some of these tubes would take short 
paths, but others stretched out far into space. As the field 
of force travels at the rate of 186,000 miles a second in the 
of a second, a field of force will be just commencing 
465 miles away. At this moment the resistance of the air- 
gap breaks down and a spark takes place. Suppose the 
natural period of oscillation of the Hertz vibrator to be 
one million a second, in 250000 a second the whole 
vibrator will be at the same potential, and immediately 
afterwards there will be a reversal of potential. During 
this 250000 a second the field of force will be shrinking, 
and the tubes within the distance of nearly a mile will 
have Vanished. With the reversal of potential a fresh 
electric field in the opposite direction is produced, repelling 
the former field into space. Suppose the damping to be 
such that the amplitude of the current in the vibrator 
at the second swing is 74 per cent, of the amplitude at the 
first swing; then, after eight half vibrations, the current 
amplitude will be only one per cent, of that at the first 
swing ; so that after 62500 of a second the vibrations are 
practically over, and the time during which no vibrations 



58 


RADIO-TELEGRAPHY. 


are taking place is over 600 times more than the time of 
the disturbance. The number of charges named would be 
of the order usually given to an electric oscillator. With 
Hertz’s oscillator the damping was probably of about this 
order, but the natural frequency of the vibrator was about 
500 times greater, so that the time during which there is no 
wave being emitted is 800,000 times as long as the duration 
of the disturbance. 

Wave-Length of Light compared ivith that of Ilertz , and the 
Waves used in Practical Radio-Telegraphy. —It would take 
us too far from the subject to fully describe Hertz’s experi¬ 
ments on the reflection and refraction of his waves, and how 
all experiments since have tended to confirm Clerk Maxwell’s 
original view that light, radiant heat, and actinic or photo¬ 
graphic rays are due to electric vibrations. The wave¬ 
lengths of light visible to the human eye vary from between 
about ioooo touoo a millimetre, whilst actinic rays 
have been measured as small as T oioo> anc ^ radiant heat 
waves as large as of a millimetre. The waves produced 
by Hertz were about sixty centimetres long, but successive 
experimenters have succeeded in producing shorter and 
shorter waves by electric means till Lampa has obtained 
waves four millimetres in length. These are seventy times 
as long as the longest heat waves experimented with, hut 
the properties of the two are most closely allied. In the 
next chapter we will consider the form of modified Hertz 
wave used in practical radio-telegraphy, which is generally 
made to have a length of from about 100 to 3000 metres. 



ELECTRO-MAGNETIC WAVES. 


59 


The Tiro Forms of Electric Oscillator .—There are two 
essentially different forms of electric oscillator. The first, 
as used by Feddersen, consisted of a Leyden jar and 
spark-gap. In this case practically the whole of the 
electric field is concentrated between the two coatings 


of the Leyden jar. The field travelling into space as the 
jar is charged is very minute, and the whole of the field 
between the coatings shrinks to nothing as the jar is 
discharged. The energy, not absorbed in heating the air- 
gap, causes a reversal of charge and electric field, which in 
this case may be nearly as great as the first. V. Bjerknes, 
experimenting with such an oscillator, found the decrement 
of damping 1 to be 0 - 01 due to a spark-gap of one millimetre, 
or the amplitude of each vibration would be 99 per cent, of 
the previous one. The damping due to other causes in this 
form of oscillator can be made negligible. The second 
form of oscillator is that of Hertz, and it will be seen that 
there is no such concentration of electric field. Some of 
the field spreads out far into space, and is consequently 
radiated as electro-magnetic waves into space as previously 
explained. V. Bjerknes measured the damping of a Hertz 
oscillator, which had a wave length of 443 centimetres. 
The damping due to radiation was 0’26, or the amplitude of 
one swing to the last before it was about 77 per cent.—that 
is, the energy radiated at each vibration is about 22 per cent. 


1 The logarithm to the base e of the ratio of the amplitude of eacli 
half swing to the next is a constant, and is called the decrement of 
damping. The decrement multiplied by twice the frequency is called 
the damping factor. 


CHAPTER IY. 


MODIFIED HERTZ WAVES USED IN RADIO-TELEGRAPHY. 

History .—The way for practical wireless telegraphy was 
prepared by numerous inventors. Munk discovered in 1835 
and E. Branly, of Paris, rediscovered, 1 in 1890, that the 
state of metallic filings was changed when placed in a 
resonating circuit in the vicinity of a vibrating electric 
current. Lodge improved Branly’s instrument and used it 
for receiving signals over a distance of 150 yards in 1894, 
and called the filings tube a coherer, as the filings cohere 
together, and become a conductor under the influence of 
the Hertz waves. Popoff, of Cronstadt, used the coherer 
in 1895, first for registering electric discharges in the 
atmosphere and later for detecting signals, obtaining good 
results over a distance of three miles. Popoff, in these 
experiments, made one most important improvement in 
that his resonator consisted of a wire carried high up into 
the air. It remained for Marconi, in 1896, experimenting 
for the British Post Office, then under the enmneerinrr 
guidance of Sir William Preece, to discover that waves 
could be detected over longer distances by prolonging one 
arm of the oscillating circuit both at the sending and 

1 See p. 1(33. 


HERTZ WAVES USED IN RADIO-TELEGRAPIIY. 61 


receiving station high into the air. This wire is now called 
the aerial or antenna. Marconi, at the same time, earthed 
the other arm of the oscillator. 

The Marconi Aerial .—It will be seen Marconi introduced 
two important modifications into the Hertz oscillator:— 

(1) Using the earth as one arm of the oscillator. 

(2) Carrying the other arm high into the air. 

By this means the distance of signalling was increased 
from one or two miles to one hundred miles. Marconi 
further found that by doubling the height of the aerial the 
distance of signalling was increased four-fold, or that the 
distance of effective signalling, other conditions being kept 
the same, was proportional to the square of the height 
of the aerial. George W. Pierce has shown that the law 
is modified according to the method of bringing the 
receiving circuit into tune. With similar sending circuits, 
if the receiving circuit is brought to resonance by capacity 
placed as a shunt to the detector, the current received is 
approximately proportional to the square of the height of 
the receiving antenna; but when resonance is obtained by 
added inductance in series with the detector, the received 
current is proportional to the height of the antenna. 

Earthing the Aerial .—It is now generally allowed that it 
is a difficult problem not to earth one arm of a commercial 
radio-telegraph oscillator, though with the original Hertz 
arrangement there was no such difficulty. Marconi and 
most of the early pioneers of wireless telegraphy believed 
it essential to obtain a good metallic and conducting earth, 


62 


RADIO-TELEGRAPHY. 


and they used the same means as employed in ordinary 
telegraphy: they connected the aerial to copper conductors 
buried in the earth. Sir Oliver Lodge, on the other hand, 
thought that the action of the earth was altogether 
prejudicial, and that the whole oscillator should be removed 
as far as possible from the earth. The Lodge-Muirhead 
Syndicate, working on this idea, found it impracticable to 
raise the oscillator out of the influence of the earth, so 
they placed the lower arm of their oscillator on the ground, 
and later a short distance above the ground, and insulated 
from it. It is now generally admitted that for land 
stations this arrangement is usually much better than the 
conductive earth of Marconi, for reasons to be hereafter 
mentioned; this insulated arm and the earth together 
form a condenser, which can be made to offer a very 
small resistance to the rapidly alternating currents used in 
radio-telegraphy. 

Theory of Earthed Hertzian Waves .—The generally 
accepted theory of the action that takes place in wireless 
telegraphy can be most readily followed by first sup¬ 
posing the earth to be infinitely conducting. Considering 
it as one arm of an oscillator, its capacity is immensely 
greater than the other arm. 

The potential of the earth will thus remain zero during 
the charge of the oscillator. The field of force during the 
charge, between the aerial and the earth, will be exactly the 
same as if it were twice the height and the earth were not 
there, and the lines of force meet the earth at right angles. 


HERTZ WAVES USED IN RADIO-TELEGRAPHY. 63 

When a spark takes place there is the shrinkage of the 
field and diminution of lateral pressure, which causes first 
a depression and then a breaking off of the tubes, as in the 
case of the Hertz oscillator, hut there is this important 
difference: with the Hertz oscillator the tubes of force were 
closed on themselves, whereas in this case they have two 
ends on the conducting plane. Consider a unit tube 
travelling off with the velocity of light; the two ends on 
the conducting surface will be unit charges, one positive 



and the other negative. Supposing perfect conductivity 
there will be no penetration. The moving charges will each 
constitute an electric current; thus taking any point on 
the earth there will be a current flowing in the direction 
the waves are being propagated, alternately positive and 
negative, with a periodicity the same as the propagated 
wave; whilst at right angles to the direction of motion 
in the plane of the conducting sheet there will be no current. 
In Fig. 40 are shown two lines of force as radiated from a 
Marconi aerial separated by half a wave-length. The 
travelling charges along the earth’s surface constitute an 



64 


RADIO-TELEGRAPHY. 


electric current. The time taken for the field to tia\el 
through the dielectric is the same as light; along the con¬ 
ductor the speed depends on the inertia and capacity of the 
earth, so that consequently there is a distortion of the field 
near the earth. The intensity of the field is less at B than 
at A for two reasons, one due to general dispersion and 
radial growth of the field from the oscillator, and secondly 
loss due to the resistance of the earth s surface. 

Pierce s Experiments .—That an earthed 
aerial behaved in a similar manner to a 
duplicated aerial was proved by Pierce 
in 1905. With a given sending station 
he made arrangements in the receiving 
_ station so that the aerial could he 

H 

switched either to a metallic earth, or to 
a horizontal wire placed three feet above 
the earth. This is shown in Fig. 41. 
The aerial A is connected through inductance L, a measur¬ 
ing instrument B, through the switch S, either to the 
earth E or the horizontal wire H, containing the induct¬ 
ance J. To obtain the maximum received current, the 
horizontal circuit had to be similar to the aerial circuit. 
Moreover, if instead of the inductance J, the wire was 
extended, the best length was a quarter of the wave length 
of the radiated waves. 

Dr. Erskine Murray's Hypothesis. —Dr. Erskine Murray 
has lately brought forward the hypothesis that the waves as 
they spread out from the oscillator impinge on the rarefied 








HERTZ WAVES USED IN RADIO-TELEGRAPIIY. 


65 


upper strata of the atmosphere, and thus eventually consist 
of tubes of force travelling between two conducting surfaces, 
one being the earth and the other the rarefied upper strata 
of air, which has been shown by Professor J. J. Thomson to 
be an almost perfect conductor. The hypothesis is of 
interest, but as the air only becomes gradually more and 
more rarefied before the upper conducting strata is reached, 
it would appear probable that considerable energy would 
be dissipated in partially conducting strata. It might here 
be pointed out that the rarefied upper strata of air being a 
good conductor would effectually prevent the possibility of 
signalling to Mars, which it is so often popularly supposed 
will be the next triumph in this field of science. 

Free Hertzian Waves .—It has been believed by a few that 
the action of the earth is prejudicial only, causing losses 
due to currents upon its surface, and that if possible it would 
be best if the whole oscillating system could be elevated high 
above the earth so that free Hertzian waves would be used. 
It is difficult to prove if this be correct. Most of the earliest 
experiments over not more than a few hundred yards were 
carried out with free Hertzian waves, and longer distances 
were not traversed till the earthed waves were employed. 
But at the same time another important change was made. 
The free Hertzian wave employed had a wave length of only 
a few metres. With the earthed system waves at first of the 
order of about 100 metres, and now for long distances waves 
as long as 3,000 metres, are used. The air is not a perfect 
dielectric. As in the case of light, it is only the long red rays 


11.T. 


F 


66 


RADIO-TELEGRAPHY. 


that can pierce a fog, so in wireless telegraphy it is found 
that for long distances, or for signalling over obstructions, 
it is necessary to employ a radiator emitting long waves. 
The whole advantage may be due to the increased wave 
length, but as it would be necessary to elevate the radiator 
high above the ground to obtain free waves, this is not 



Eig. 42. 



practicable. Dr. Muirhead has lately found that to obtain 
best syntony the aerial should be removed from the earth 
a certain fixed distance ; removing it further, the radiation is 
reduced. Moreover, Lodge now considers that earthing the 
aerial may he best for long distance signalling for untuned 

stations, where interference is of no 
importance. 

Earthed Waves with Surface not per¬ 
fectly Conducting .—It has been pointed 
out that in the generally accepted theory 
of wireless telegraphy the electric field 
consists of tubes of force terminating’ 
in charges on a conducting surface; if the surface be a 
perfect conductor, the field and charges expand from the 
radiator with the velocity of light, and these moving charges 
are electric currents. However, the earth is not a perfect 



conductor, so that there is penetration and consequent dissi¬ 
pation of energy as heat, accompanied by a lag of the current 


HERTZ WAVES USED IN RADIO-TELEGRAPHY. 67 


behind the field. Associated with this current are its electric 
and magnetic fields. The combined electric field is there¬ 
fore rather tilted forward from the earth’s surface, as was 
shown in Fig. 40. 

The Radiated Magnetic Waves .—As with the Hertz waves, 
the magnetic field does not circle round the current. 
Looking at a single moving tube of electric force T, in 



plan, a line of magnetic force may he represented by a 
circle round it as in Fig. 42. Next consider two adjacent 
tubes (Fig. 48); when these are quite close together the 
lines between them being in opposite directions cancel, 
and the magnetic field becomes a series of closed curves 
round the two tubes (Fig. 44). Next take a circle of tubes, 
all moving away from the centre (in this case the axis 
of the transmitter) : it will be seen the curves of Fig. 44 
become two circles of magnetic force (Fig. 45), embracing 

f 2 







68 


RADIO-TELEGRAPHY. 


the circle of tubes of electric force. Then suppose a second 
circle of tubes (Fig. 46) spreading out close behind, the fields 
between cancel each other. With different strength of field, 
however, as in the case of a radiated wave, the two circles 
C C 2 do not cancel, and we get finally a series of circles 
(Fig. 47) which represent the differences of magnetic field 
due to circles of electric tubes following each other and of 
slightly different strength. It will thus be seen that, at a 



Fig. 47. 


given time and place, the current is radiating in all direc¬ 
tions along the conducting surface from a fixed point, viz., 
the position of the radiator; so that the lines of magnetic 
force due to the currents in the conducting surface, as well 
as those of the travelling field, will be circles round the 
radiator. 

Obstructions, Inequalities, and Curvature of the Earth .— 
If a stone he thrown into a smooth pond the ripples will be 
seen to spread out in all directions, and if a small obstruc¬ 
tion be placed in their path, just behind the obstruction 
there will be smooth water, but a little way further on the 
ripples will curve round and progress apparently as if 








HERTZ WAVES USED IN RADIO-TELEGRAPHY. 69 


nothing had obstructed them. It is extremely difficult to 
notice this effect with light, but it is very noticeable with 
the waves we are considering. Jackson was the first to 
observe how signals vanished when high land intervened 
between two ships, one ship being close under the land. 
Suppose a perpendicular conducting body, such as a tree, 
be in the path of the waves, the field, striking this con¬ 
ducting body, causes a current to flow on the side of the 
tree facing the radiator, with consequent loss of energy. 
There will be a certain amount of radiation possibly from 
the tree back towards the radiator, and a consequent distor¬ 
tion of the field. This distortion is only quite close to the 
tree, and the wave continues as if nothing had happened, 
but with slightly diminished energy. Next consider a 
gradual slope of conducting material. The whole of the 
energy striking the slope will be given up to the conductor. 
Some of this energy will be dissipated and the rest will be 
returned, and the electric field due to the current on the 
surface of the earth will be at right angles to the slope, 
so that there is a tendency for the electric field of the 
moving wave to be always at right angles to the earth’s 
surface. The form of the waves over hilly and wooded 
country must be extremely complicated, and it requires 
considerably more energy at the transmitting station to 
signal over land than over sea, the extra amount depending 
on the character of the soil, the amount of forest land, and 
the hilliness of the country. It is usually stated that under 
ordinary conditions the amount of power required to signal 


70 


RADIO-TELEGRAPIIY. 


over land is from three to ten times that over sea, but in 
certain cases it may be much more. It is evident that the 
worst condition is when a mountain rises close to either the 
sending or receiving station and between them. Probably 
in such a case the hill acts as a mirror, almost completely 
reflecting the waves. The curvature of the earth will also 
cause loss in the same way as a change of slope, but it has 



Fig. 48. 


been pointed out that if it is possible to signal half (180°) 
round the globe, after that there will be conflux of energy 
towards a point immediately opposite the transmitting 
station. 

Experiments on the Screening Action of Obstructions .— 
Very careful experiments were carried out by Messrs. 
Duddell and Taylor in Bushey Park, 1904, for the Postal 
Telegraph Department, at the instance of the engineer-in- 
chief, Mr. J. Gavey, and later in the Irish Channel, in the 
































HERTZ WAVES USED IN RADIO-TELEGRAPHY. 71 


vicinity of the Hill of Howth. In the Busliey Park experi¬ 
ments the receiver aerial was 56 feet and the transmitter 
aerial 42 feet high; the wave length at both stations was 
400 feet, the spark gap 7'08 mm., and the current in 
the transmitting wire varied from 0'5 to 0*56 amperes. 
The current in the receiving wire was measured by a 
Duddell thermo-galvanometer, the position of the receiver 
was kept fixed, and the transmitter was moved. One of the 
curves giving results obtained is reproduced in Fig. 48, 
which shows the product of current and distance for different 
distances from the transmitter. The position of the 
trees is depicted. The screening action of the trees is 
very marked, as well as the rapid improvement as the 
receiver was moved further out of the influence of 
these. 

According to tests carried out by F. Braun, neighbouring 
obstacles always have a screening action even when they 
are behind the radiator and acting as a reflector. F. Braun 
gives an easy method of demonstrating this fact for a closed 
oscillating circuit acting on another similar circuit. It is 
found that a sheet of tinfoil will diminish the action on a 
secondary coil equally well if it be placed either behind 
a flat primary coil or between the primary and secondary 
coils. 

Trees as Aerials .—Major S. 0. Squier, of the United 
States Signal Corps, has used trees as receiving aerials, and 
has received messages over a distance of thirty-two miles. 
The roots formed a good earth, and he made connection to 


RADIO - TELEGRAPHY. 


the tree by driving in nails. The detector was a shunt to a 
portion of the tree. 

Dissipation of Energy due to Light. —Professors Elster and 
Geitel, and independently Professor Eighi, found that bodies 
with high potential charges of negative electricity became 
de-electrified under the influence of light. Marconi, in 1902, 
put it down as probably due to this cause that he could not 
receive signals from Poldhu out at sea more than 700 miles 
during the day, hut the signals were clearly decipherable up 
to a distance of over 2,000 miles by night. He noticed 
further that the signals rapidly weakened as daylight 
increased at the sending station. This effect has not been 
noticed except in the case of long-distance transmission. 
It is, however, more probable that the principal loss due to 
sunlight is owing to it ionising the air and so making it 
slightly conducting. 

According to Fessenden, the strength of signals received 
at Washington in June at midnight and midday were in 
the ratio of 1,200 to 30 ; he, however, claims that now 
(1907) he has been able to radiate energy by a new method, 
so that the night signals are decreased to 80 and the day 
increased to 76. This method probably consists in using 
waves of the order of 3,000 metres. 

Dissipation of Energy due to Conducting Particles in the 
Air. —Captain L. D. Wildman, of the United States Signal 
Corps, carried out experiments for over a year in Alaska 
with stations 107 miles apart, and aerials consisting of two 
insulated wires 200 feet high. He tabulated as far as 


HERTZ WAVES USED IN RADIO-TELEGRAPHY. 


73 


possible the atmospheric conditions and the relative amount 
of energy received, and found that this varied approximately 
inversely as the wind velocity and amount of moisture in 
the atmosphere. Captain Wildman thought the result was 
due to the wind taking energy from the receiving aerial, but 
the loss was more likely due to increased conductivity of the 
air due to the suspension of conducting particles in it. 

Energy Received. —Messrs. Duddell and Taylor, in 1904, 
carried out numerous and careful experiments to compare 


'I 



C3 

£ Distance between Transmitter and Receiver in mites . 


Eig. 49. 

how the energy received varied with the distance of trans¬ 
mission. When there was no outside disturbing cause, they 
found, after a short distance from the transmitter, that the 
product of the current and the distance was a constant ; 
that is, the energy received varied inversely as the square 
of the distance. These experiments were carried up to a 
distance of sixty miles, and the results of one set are shown 
in Fig. 49. Tissot, in France, with another system of trans¬ 
mitting and different measuring apparatus, obtained similar 
results over distances from three-quarters of a mile to 
























74 


RADIO-TELEGRAPHY. 


twenty-five miles. In both cases the surging current in the 
transmitting aerial was about 2*8 effective amperes, and 
at a distance of thirty-five miles the current varied from 
120 to 200 micro-amperes, depending on details of trans¬ 
mitting. That is, at a distance of twenty-five miles the 
surging current in the receiving aerial is about one-fifteen 
thousandth part of the surging current in the transmitting 
aerial, or the energy in the transmitting aerial is more than 
200,000,000 times greater than that in the receiving aerial. 

Distance of Transmitting Signals .—These experiments were 
carried out over a comparatively short distance, but a large 
number of disturbing causes have been indicated which tend 
to lessen the energy received, and these only become apparent 
over longer distances. The most constant results can be 
obtained over sea, but even then, with all the working con¬ 
ditions at both sending and receiving stations apparently 
the same, signals can be received at a distance of 1,000 miles 
for a time, but shortly afterwards, perhaps, only at 200 miles. 
When this is realised it can De better understood how 
extravagant claims of long-distance transmission are so 
often misleading, and that to substantiate the claim good 
working signals should be received under the most un¬ 
favourable conditions, which are usually at midday during 
hot sultry weather. The best published results are those of 
the system between the Andaman Islands and Burma, where 
rather less than one horse-power is used for a distance of 
about 300 miles. 

Lodge has pointed out that with a similar transmitter and 


HERTZ WAVES USED IN RADIO-TELEGRAPIIY. 


75 


receiver the ratio of the received to the emitted energy 
theoretically depends on the cube of the linear dimensions 
of emitter and receiver, as well as on the cube of the distance 
between them. In one special instance he has confirmed 
this, in which case the emitted energy was 100,000,000 
times as great as the received energy. 

Difficulties of Signalling at Dawn and Sunset .—Marconi 
has lately pointed out that greater difficulty is experienced 
in transmitting signals across the Atlantic in the morning 
and evening than during day or night. He considers this 
may be due to reflection or refraction of the waves at the 
boundary between the sun-lit and the non-illuminated air. 


CHAPTER Y. 


APPARATUS USED FOR CHARGING THE OSCILLATOR. 

History .—In practice three methods of charging the 
oscillator have been used, but there are other methods 
in the experimental stage. Hertz used an induction coil, 
and this is still used for short-distance signalling. De 
Forest used an alternate current transformer, and this 
method was brought prominently before the public during 
the war between Japan and Russia, as the Times news¬ 
paper was very successful with this apparatus. The latest 
practical development is due to Poulsen, of Copenhagen, 
who in 1906 made use of the musical arc. 

The Induction Coil .—An induction coil (Fig. 50) consists of 
a core of thin iron wires surrounded by one or two layers 
of fairly stout copper wires forming the primary winding. 
Round the primary circuit is a thick layer of insulating 
material, and then many thousands of turns of very line 
insulated copper wire forming the secondary winding. 
This winding ends in two terminals, which are connected 
to the two arms of the oscillator close to the spark gap. 
The primary circuit is connected through an interrupter, 
reversing switch, transmitting key, and switchboard to 
the source of electric supply. In Fig. 51 the number of 


APPARATUS USED FOR CHARGING THE OSCILLATOR, 77 

\ 



Fig. 50 




















































78 


RADIO-TELEGRAPHY. 


primary cells B can be regulated by the switch R. The 
connexions are made through a double pole fuse F F, 
ammeter A, switch S, to the induction coil, the voltmeter 
Y being for the purpose of measuring the pressure. The 
commutator D enables the current to be reversed through 
the primary of the coil F. At rest the platinum contacts 
Pj P 2 make contact. When the circuit is completed by means 
of key K, the current from the cells magnetises the iron 
core placed inside the primary winding; an iron armature 

attached to Pi is attracted to 
the iron core, and the circuit 
is broken. A large part of the 
energy is then transferred to 
the secondary winding G, 
causing a flow of current to 
earth, and at the same time 
charging the aerial J till the 


=:b 



G 


Y 

J 


K 


3H 


Fig. 51. 


difference of potential is suffi¬ 
cient to cause a disruptive discharge across the spark gap H. 
Some of the energy is wasted in sparking across the con¬ 
tacts P, but this is mitigated to a great extent by the 
condenser C ; most of the energy that would be wasted 
in this spark, causing damage to the contacts, is absorbed 
in charging the condenser. 

When the circuit is completed the first rush of current 
charges the condenser; and owing to the self-induction of 
the primary winding, the current rises to a maximum 
comparatively slowly, so that the inductive action on the 


























APPARATUS USED FOR CHARGING THE OSCILLATOR. 79 

\ 

secondary is slight, and no disruptive discharge takes place ; 
in this case both the condenser and the self-induction of 
the coil help to prevent a quick rise of current through the 
primary. On the other hand, when the circuit is broken, 
the condenser quickens the discharge from the coil, so that 
sufficient energy is transferred to the secondary to cause 
the required spark. 

To utilise the energy of the coil as much as possible, 
Professor Ewing showed in 1880 the importance of the 
make and break of the circuit being sudden, and Lord 
Rayleigh has proved that if the break could be made 
sufficiently quick the action of the condenser would be 
deleterious. 

Bating of Induction Coils .—Induction coils are generally 
rated by the length of spark they will give between two 
terminals with no capacity in circuit. A coil suitable for 
Rontgen rays working would give a spark of from ten to 
twenty inches ; but such a coil would be unsuitable for 
radio-telegraphy unless it would give, say, a spark of quarter 
of an inch, with a capacity of one hundredth of a micro¬ 
farad across the terminals. The tendency has been lately 
to use a smaller spark, charging a large capacity to a com¬ 
paratively small difference of potential; it will thus be seen 
in this case the function of the induction coil is not to pro¬ 
duce a large difference of potential in the secondary circuit 
but a large quantity of electricity. It would seem probable 
that to obtain the best results the induction coil should be 
expressly designed for the oscillator it has to charge. 


80 


RADIO-TELEGRAPHY. 


The Telefunken Induction Coil .—Die Gesellschaft fur 
drahtlose Telegraphie in their Telefunken system use a 
thicker wire in the secondary than is generally employed, 
and it is built so that the primary and secondary circuits 
have the same oscillation constant, viz., a frequency of fifty 
cycles a second in each case. Small oscillations are at first 
set up in the secondary circuit, increasing in amplitude as 
more energy is supplied from the primary circuit till the 
discharge takes place. 

The Interrupter .—When such an induction coil is used 
with large currents the circuit has to be broken at definite 
intervals, and very quickly, so a separate motor is required 
to make and break the contacts. Usually the contact is 
made between metal and mercury, and the disadvantage of 
the arrangement is that it requires considerable attention 
to keep the interrupter working well; in consequence 
this type has, except in Germany, been mostly used for 
experimental work. With a small current a simpler 
arrangement can be used; this is to make the interrupter 
self-acting. Two platinum contacts are normally touching, 
one is stationary and the other is attached to a piece of 
soft iron at the end of a steel spring,; the growing current 
in the primary coil acts as an increasingly powerful magnet 
attracting the iron core, and momentarily breaking the 
circuit. This form of interrupter has been successfully 
used for currents of ten amperes. 

The author has found the latest type of interrupter 
employed by Mr. H. W. Sullivan very satisfactory. The 


APPARATUS USED FOR CHARGING THE OSCILLATOR. 81 


ai mature J (Fig. 52) is fastened to an upright spring F 
fixed in position. The break is made at platinum contacts 
Pi P 2 , the armature being attracted towards the coil in the 
direction of the arrow. The contact is regulated by the 
screw A, which is locked in position by the nut B. The 
feature of this interrupter is the adjustable spring E, 
whose pressure against F can be regulated by the screw C, 
the spring moving as a whole along the guide pm H, so 
that however adjusted the two 
jneces of platinum make good 
contact when touching. 

Apparatus used for working 
Induction Coils .—In Fig. 51 the 
coil is shown working with a 
primary battery. For practical 
work the dry cell is probably the 
most convenient, but is too un¬ 
reliable ; the bichromate battery would be more economical. 
For very intermittent or experimental working with a coil 
taking say two amperes, a battery of twenty cells rated at 
ten amperes would be sufficient, with a spare battery to be 
used in parallel if necessary. Such an arrangement would 
be the most economical for signalling over distances of about 



Fiff 52 


fifty sea miles. 

For longer distances up to about 100 miles, when more 
than three amperes would be necessary, a small oil engine, 
dynamo and accumulators are advisable, as shown in Fig. 53. 
The shunt wound dynamo D, with field coils W, and 


K.T. 


G 






























82 


RADIO-TELEGRAPHY. 


regulating resistance L, is used for charging a battery of 
about ten accumulators B, the battery when charged being 
used for working the induction coil. The two-way switch 
S allows the accumulators to be connected to the dynamo 
for charging, or the induction coil for discharging; the 
ammeter A measures the current, and the fuse F protects 
the battery. 

The switch R regulates the pressure supplied to the coil, 


which is measured by 
the voltmeter V. This 
arrangement would in 
general be satisfactory 
for about 100 sea miles. 
If instead of ten cells, 
forty or fifty cells are 
used, and a resistance 
placed in the induction 



Fig. 53 . 


coil circuit, sufficient to reduce the current to ten amperes, 
the extra pressure is found to increase the signalling dis¬ 
tance to 150 miles or more. 

Arcing between Spark-knobs .—This is only troublesome 
when the capacity is too small and the discharge commences 
at the same time as energy is still being given to the 
oscillating circuit from the induction coil, so that the current 
persists for a longer time than the natural period due to 
energy supplied directly across the gap from the coil. The 
trouble can to a certain extent be remedied by the arrange¬ 
ment of the air-gap; but when this cannot be further 






























APPARATUS USED FOR CHARGING THE OSCILLATOR, 83 

\ 

improved it is necessary to decrease the energy given at 
each charge. This is done by increasing the number of 
charges per second, increasing the speed of the motor 
interrupter, or weakening the tension of the spring with 
the hammer make and brake. This latter operation also 
has the effect of increasing the number of interruptions per 
second. Arcing is only likely to occur with open circuit 
systems, as is explained in a subsequent chapter, and it is 
more troublesome with induction coils than transformers. 
Bad arcing is easily distinguishable by the spark assuming 
a red furry character. The spark to be aimed at is thick, 
intense white, and has a sharp crackly sound. 

The Lodge Value .—For military purposes a great deal is 
sacrificed to lightness, and to obtain this the Lodge- 
Muirhead Syndicate use an electric valve or specially made 
vacuum tube. Two valves 1 are necessary, and these are 
placed between the secondary and the spark-gap. The 
action of this valve is to allow current to flow only in one 
direction, so that it permits energy to be accumulated in 
the oscillator during a number of interruptions of the 
induction coil, till the potential of the aerial can be made 
as great as the maximum potential furnished by the coil. 
This enables a small and light coil to be used. It will be 
seen the valve is useful when the capacity to be charged is 
too large for the coil, but it probably also protects the coil 
from breakdown due to oscillatory currents. 

Alternate Current Transformer .—This is a similar piece 
The two valves are shown in Figs. 163, 164, Chapter XIV. 

Q 2 


i 


84 


RADIO-TELEGRAPHY. 


"'S —isi— vwv®-^- 

P L C 

—is—vwv 


of apparatus to the induction coil; but, instead of direct 
currents being made pulsating by an interrupter, alternating 
currents are employed so that no interrupter is required. 
The following arrangement is suitable for a small station 
of several horse-power. In Fig. 54 the alternator J has 
its field F magnetised by means of the direct current 
dynamo D on the same shaft, S being the dynamo field 
coil, and R x R 2 adjustable resistances in the fields of the 
alternator and exciter respectively. The current from the 

alternator passes 
through a double pole 
switch P, fuse L, and 
adjustable choking 
coils C, ammeter A, 
transmitting key K, 
and the primary of 
transformer T. The 
alternator is pro¬ 
tected from oscillatory current by means of condensers 
connected to earth, and the transmitting key is shunted by 
a condenser M to prevent excessive sparking. 

The Lodge-Muirhead Transformer and Alternator .—The 
latest type of transformer made by the Lodge-Muirhead 
Syndicate is of the open magnetic type, and the primary is 
wound on a straight bobbin of finely divided wires. The 
circuit, consisting of the aerial and the secondary of the 
transformer, has the same oscillation constant as the circuit 
of the alternator and primary winding, this frequency being 




Eig. 54. 














APPARATUS USED FOR CHARGING TIIE OSCILLATOR, 85 


necessarily low. When the discharge takes place the 
secondary of the transformer is short circuited by the low 
resistance spark, and the frequency of the oscillations is 
high, depending only on the capacity and inductance of the 
aerial circuit. To prevent breakdown the secondary of this 
transformer is wound in unit coils of 250 watts 1 connected 
in series. 

In ordinary alternators such as are used in electric 
light systems the designer tries to obtain a sine curve con¬ 
necting current with time (see 
Fig. 21), but in a radio-tele¬ 
graph alternator it is important 
to keep the current charging 
the aerial at a maximum as 
long as possible, and this is 
done by aiming at a curve of 
the nature shown in Fig. 55. An alternator of this type 
is now used in the Lodge system. 

For closed systems, where large capacities have to be 
charged, a low frequency, such as 50 periods, is generally 
employed, but with open circuits and smaller capacity as 
high a periodicity as 200 has been used to avoid arcing, as 
will be explained later. 

High Power Apparatus . — When the signalling distance is 
over 500 miles, and at the same time it is necessary to have 
a sharply-tuned transmitting station to avoid interference 
with other systems, about 30 or more horse-power has to 

1 7R3 Watts = 1 liorse-power. 








RADIO-TELEGRAPHY. 


be used. With an open circuit the aerial would probably 
have to be a quarter of a square mile or more in area, 
and with coupled circuit systems two difficulties occur; 
the capacity in the closed circuit and the radiating surface of 
the open circuit have both to be made enormously large. 
To obviate this Professor Fleming, in 1900, used a subsi¬ 
diary oscillatory circuit of intermediate frequency. By this 
means instead of charging the oscillatory circuit about 200 
times a second he was able to charge it as often as 20,000 


times a second, allowing the 
condenser and radiating sur¬ 
face to be one fiftieth of the 
size which otherwise pro¬ 
bably would have been 
required. In Fleming’s 
arrangement a 2,000 volt 


c D 


p 



Eig. 56. 


alternator at 100 periods supplies current which is raised 
to a pressure of 20,000 volts by the transformer A (see 
Fig. 56). The rotating arm B comes alternately within 
sparking distance of the sectors C and D, first closing the 
circuit A C F for sufficient time to allow the condenser F to 
be fully charged, and then completing the circuit GDF 
through the primary of a second transformer; during which 
time the condenser is discharged, the natural periodicity of 
both circuits being about 10,000 a second. This discharge, 
acting through the transformer G L, charges the condenser 
P, and this in turn is discharged through the spark-gap B, 
setting up oscillations in the radiating circuit. 










APPARATUS USED FOR CHARGING THE OSCILLATOR. 87 


It will be seen there are six circuits :— 

(1) Alternate current circuit at low frequency and 
pressure. 

(2) Intermediate circuit A C B F charging condenser F. 

(3) Intermediate circuit B I) G F discharging con¬ 
denser F. 

(4) Closed circuit L P Q charging condenser P. 

(5) Closed high frequency circuit P Q R discharging 
condenser P through spark-gap R. 

(6) Radiating circuit. 

The function of all this is fundamentally the same as 
reducing the tension of the spring of the interrupter in the 
induction coil, namely, it allows a larger number of smaller 
impulses to be radiated. 

Protection of Apparatus .—If the frequency of the circuit 
containing the secondary of the induction coil or trans¬ 
former and the spark-gap approaches that of the oscilla¬ 
tory circuit, there is a danger of breakdown. For pro¬ 
tection, choking coil are often inserted between the 
secondary and the spark-gap. The generators are also 
liable to break down from oscillations set up in the connect¬ 
ing wires, so it is customary to connect each terminal to 
earth through a Leyden jar (Fig. 54), the condenser offering 
a path of infinite resistance to the direct current of a 
dynamo or the low frequency current of an alternator, and 
at the same time short circuiting them from the high 
frequency oscillations. 

The Musical Arc .—In 1892 Elihu Thomson discovered 


88 


RADIO-TELEGRAPHY. 


that electrical oscillations could be produced by shunting 
an air-gap in a continuous current circuit with capacity 
and inductance. Duddell, in 1900, using the ordinary con¬ 
tinuous current arc lamp, shunted this with suitable 
capacity and inductance, and measured frequencies of 
50,000 per second, too low, however, to admit of radiation. 
It remained for Poulsen, using an arc between carbon and 
copper in hydrogen, to obtain frequencies of 1,000,000 per 
second, and show the possibility of radiating a practically 
continuous supply of energy into space. There seems no 
doubt that with the Poulsen apparatus as now made, a 
practically, though not perfectly, continuous train of waves 
is produced, and that remarkably good results have been 
obtained, though it is not yet apparent how far the appara¬ 
tus is reliable for everyday working. Professor Fleming 
has given it as his opinion that at present it is difficult to 
erect and adjust the Poulsen arc, and that moreover it can 
only be made to absorb neither more nor less than about 
two horse-power. According to Duddell, to produce the 
oscillations, it is necessary that the rate of change of 
potential with current across the arc should be negative 
and greater numerically than the resistance of the oscilla¬ 
tory circuit. 1 Whilst current is flowing into the condenser 
the potential difference across the arc is increasing, causing 

1 If at any moment, Y is the potential difference across the arc, C the 
current through the arc, and r the resistance of the shunt circuit, 
oscillations occur when :— 

d Y 


APPARATUS USED FOR CHARGING THE OSCILLATOR. 89 


a further charging of the condenser. On the other hand, 
when the condenser discharges through the arc, the 
increased current quickens the rate of decrease of the 
potential difference. Simon found that higher frequencies 
were obtained by increasing the current through the arc or 
decreasing the length of the arc; these results have been 
confirmed by Austin. Austin has also obtained equally 
good results with the arc in steam as in hydrogen. The 
action of the hydrogen appears to be partly due to its greater 
conductivity compared with air, thus 
helping to cool the arc electrodes. 

Poulsen also considers that the hydro¬ 
gen increases the conductivity of the 
arc. 

The Cooper-Hewitt Mercury Inter¬ 
rupter as a Radio-telegraph Discharger .—Hewitt has used a 
special form of his mercury vapour lamp to take the place 
of the spark-gap in an oscillating circuit. In Fig. 57 an 
exhausted bulb I, about 6 to 8 inches in diameter, has 
two depressions containing pools of mercury between which 
the discharge takes place. Pierce has shown that if the 
vacuum is too high the discharge cannot readily be started, 
and if it is too low the vibrations are feeble, and there is a 
tendency for an arc to form in the bulb. Current may be 
obtained through an ordinary alternating current trans¬ 
former P charging the condenser C. When the difference of 
potential between the coatings become sufficiently high the 
resistance of the interrupter drops to a fraction of an ohm 7 











90 


RADIO-TELEGRAPHY. 



Pig. 58. Fig. 59. 


and an oscillatory dis¬ 
charge takes place through 
the Tesla transformer T. 1 

As the oscillations be¬ 
come weaker the tube 
becomes non-conducting, 
and the condenser is again 
charged. Pierce has 
thoroughly investigated 
the behaviour of this form 
of discharge. With a 
particular interrupter he 
found the discharge always 
began to occur when the 
difference of potential of 
the condenser reached 
7,070 volts, and the dis¬ 
charge continued till the 
pressure was reduced to 
1,600 volts. By using a 
small Leyden jar and a 
charging potential of 
15,000 volts he obtained 
200 complete discharges 
during T | 0 of a second, 

1 For arrangement of oscil¬ 
latory circuits, see succeeding 
chapters. 





APPARATUS USED FOR CHARGING THE OSCILLATOR. 91 


the one half cycle of the charging transformer; that is, 
he obtained 24,000 trains of vibrations a second, and 
each discharge was separated by an interval of xooooo 
of a second. With a larger capacity, 0‘01B mf. about 
1,440 discharges were obtained per second. By photo¬ 
graphing the spark Pierce showed that in the case of the 
ordinary spark-gap from a transformer, the discharges 
were spasmodically strong and weak, due to the spark-gap 
retaining its conducting character too long; but with the 
vacuum tube every discharge was sharp, definite, and 
regular. In Fig. 58 are given two photographs of successive 
discharges with ordinary spark-gap under best conditions, 
using cadmium knobs, and Fig. 59 is a photograph of 
successive discharges with the vacuum tube. 

The resistance of the tube decreased with increased 
condenser capacity, and increased with added inductance 
in circuit. The following results are typical :— 

Table showing Change or Resistance of Mercury Interrupter 
with Capacity. Inductance = 0-000117 Henry. 

Capacity in microfarads ... 0*0130 0-313 0*730 0-117 

Period, millionths of a second 7*76 12-1 18-6 23-5 

Resistance in ohms ... ... 0*37 0*44 0-24 0 - 20 

Table showing Change of Resistance of Mercury Interrupter 
with Inductance. Capacity 0-0730 Microfarads. 

Inductance in millihenrys ... ... 0-0110 0-117 1-4 2 

Period, millionths of a second ... 0’14 18 - 6 04-7 

Resistance in ohms ... ... ... 0*14 0-24 0-G0 

Vreeland’s Modification of the Mercury Interrupter .— 
Vreeland has used a mercury vapour tube to obtain 


92 


RADIO-TELEGRAPHY. 


continuous oscillations. As will be seen from Fig. 60, the 
tube containing mercury vapour has two metal anodes 1 and 
one mercury cathode. Direct current from cells is used, 
and variations in the current between the two anodes and 
the cathode cause oscillations to be set up. It is to be 
noted that the two coils next the tube are placed, not as 
shown in diagram, but so that the magnetic field is perpen¬ 
dicular to the plane of the anodes. Choking coils are 
placed in the battery circuit. The circuits are never 

exactly symmetrical, so that current 
tends to flow more through one 
arm than the other. The action 
is intensified by the coils which 
deflect the current, so that the 
whole or most of the current flows 
through one anode. When the 
condensers are charged the current is reversed, the coils 
deflecting the current to the second anode, and according to 
Vreeland the energy is fed to the oscillatory circuit in 
synchronism with the vibrations. 

The High Frequency Alternator .—A great many attempts 
have been made to obtain undamped oscillations by employ¬ 
ing an alternator having a frequency sufficient to enable it 
to be utilised so as to produce oscillations direct without the 
intervention of a spark or an arc. This arrangement has 
been successfully employed by Fessenden. He makes 
alternators, driven by De Laval steam turbines, having 

1 See footnote p. 174, 



Fig. 60. 





























APPARATUS USED FOR CHARGING THE OSCILLATOR. 93 


frequencies of about 100,000 periods per second. Single¬ 
wound armature machines have an approximate output of 
1 k.w., and double armature machines 2 k.w. Fessenden 
gives for the single armature type the open circuit pressure 
of 150 volts, field current 5 amperes, and resistance drop in 
armature 6 ohms, with a similar inductance drop, which is, 
however, neutralised by capacity, and so has no effect on the 
output. The double armature machine gives 270 volts on 
open circuit, and the armature has a resistance of 9 ohms. 

When used for radio-telegraphy the continuously gene¬ 
rated waves are broken into groups. This would prevent 
the cancelling effect that has been noticed when continuous 
waves are produced. 

The Spark or Arc, in Compressed Air .—Following Fes¬ 
senden L. W. Austin has used direct current from a source 
of 4,500 volts in series with a 30,000 ohm resistance and a 
spark-gap of 0*4 mm., the current being rather less than 
-J ampere. The spark takes place in compressed air, the 

gap being shunted by capacity and inductance. Oscillatory 

\ 

surgings occur in rapid succession when the pressure round 
the spark is about 6 atmospheres; and several hundred 
ohms might be inserted in the oscillatory circuit. When 
oscillations occur the current through the gap decreases 
slightly and the potential difference at the terminals 
increases twentyfold. Austin also found that the greater 
the heat conductivity of the spark-knobs the better were 
the results obtained. 


CHAPTER VI. 


THE ELECTRIC OSCILLATOR-METHODS OF ARRANGEMENT. 

History .—The greatest advance from the Hertz oscillator 
was that made by Marconi in 1896. He used a conducting 
wire carried high into the air as one arm of the oscillator, 
whilst he connected the other arm to earth. For some 
time progress was made in two directions—(1) Increasing 
the height of the aerial wire; (2) loading the aerial wire 
with capacity. At first Marconi experimented chiefly in 
the first direction. Sir Oliver Lodge believed in the second. 
He had shown in 1896 how oscillations in one Leyden jar 
circuit could be made to set up oscillations in a secondary 
circuit. He found that it was necessary to have the oscilla¬ 
tion constants of the two circuits made more nearly 
alike than in the Hertz arrangement; in the case of the 
Leyden jar oscillator the vibrations were both more per¬ 
sistent, and the waves emitted were of one definite frequency, 
but it was not until 1897 that he patented an intermediate 
form of oscillator consisting of large cones or plates far 
apart, a system that has been successfully developed by the 
Lodge-Muirliead Syndicate. The next improvement was 
due to F. Braun, of Strassburg, who in 1898 was the first 
to use two circuits, the closed Leyden jar circuit of Lodge 
giving a persistent train of oscillations coupled to the 
Marconi aerial which quickly radiated the energy given it. 


THE ELECTRIC OSCILLATOR. 


95 


From 1898 to 1906 great progress was made both in details 
of arrangement and manufacture, and in the last named 
year Marconi made practical the use of a long horizontal 
wire some distance above the earth. This gives a partly 
directional character to the radiation. In 1907, Bellini and 
Tosi discovered that any closed circuit placed in a vertical 
plane gave this directive radiation. 

Systems of Transmitting .—All the following arrangements 
are now used in practice:— 

(1) Single aerial or antenna. 

(2) Aerial loaded with capacity. 

(8) Aerial circuit coupled through auto-transformer to a 
closed oscillatory circuit. 

(4) Aerial circuit coupled electro-magnetically through 
Tesla transformer to a closed oscillatory circuit. 

(5) Multiple coupled systems with aerial circuit coupled 
through transformer to two or more closed oscillatory 
circuits. 

(6) A horizontal wire above the earth’s surface forming 
either a single oscillatory circuit or coupled through a 
transformer to a closed circuit. 

(7) A closed radiating circuit in a vertical plane either 
single or coupled. 

Single Aerial or Antenna .—On account of its simplicity 
the single open-circuit aerial of Marconi has much to 
recommend it as a transmitter. It is diagrammatically 
shown in Fig. 61. 1 The antenna A is taken high into 

1 It will be noticed that oscillatory circuits are shown in thick 
lines, other circuits in thin lines. 


96 


RADIO-TELEGRAPHY. 


V 


B 


B 


the air and is kept well insulated. It is connected through 
the spark-gap G to the other arm of the oscillator, which 
is the earth, through the earth-plate E. The two thin lines 
B B are the wires from the induction coil. The capacity 
and self-induction of the earth is constant. The capacity 
and self-induction of the aerial varies directly with the 
length, hence the longer the aerial the greater is the energy 
that can be stored and the longer the wave-length. Different 
values have been given for the wave radiated by 
such an aerial, varying between four and five times 
the total length. It is probable that the discre¬ 
pancies are due to minor details of arrangement. 
In practice it is always best to arrive at the wave¬ 
length by actual measurement, in the manner to 
be explained in a subsequent chapter. 

Disadvantages of the Single Aerial .—There are, how¬ 
ever, a number of disadvantages in using a single aerial 
circuit. 

(1) The capacity of the aerial cannot be made large, and 
therefore it requires very little energy to charge it to a 
given potential. 1 In other words, it is incapable of taking 
up much energy at a time, to transform into radiations. 
The student has to clearly grasp the idea that radio¬ 
telegraphy is a system of transmitting energy. The actual 
energy received is indeed minute, but to obtain this minute 
energy at the receiving end a large quantity of energy has 


Fig. 61 


1 A wire one-tenth of an inch in diameter would have to be 500 feet 
high to store the same energy as a pint Leyden jar, of which the 
capacity would be about 0*001 mf. 







THE ELECTRIC OSCILLATOR 


97 


to be radiated for long distance working. It is an easy 
problem to-day to generate several hundred electrical horse¬ 
power, but it is extremely difficult to radiate the energy. 
It is this problem that is being worked at by the principal 
radio-telegraph companies. AYhen energy can be satis¬ 
factorily radiated at the rate of, say, one hundred horse¬ 
power, it is probable that a few millionths of a horse-power 
will be received with certainty at the other side of the 
Atlantic. Using the single aerial circuits less than a 
quarter of horse-power can be utilised, which is sufficient 
for distances of one hundred miles over sea. 

The energy stored can be increased by lengthening the 
spark-gap, but the resistance is more than proportionally 
increased so that the total energy radiated is reduced. 

(2) For long-distance and over-land transmission it is 
found best to employ a long wave-length. With the single 
aerial it is not usual to attempt a greater wave-length than 
200 metres, with aerials 100 to 120 feet high. 

(8) According to Zeneck the damping of the single aerial 
wire, due to radiation only, is of the order 0'8, so that after 
about fifteen vibrations the amplitude will be one hundredth 
of the maximum. For short distances, if there is no fear 
of outside disturbances, this is an advantage, as with a 
given amount of energy the amplitude of the first vibration 
is much larger, causing a greater radiation of energy and 
greater amplitude of first swing in the receiving circuit; 
but it will be explained later how a receiving circuit which 
is acted on by one surge of electric energy is acted on by 


R.T, 


H 


98 


RADIO-TELEGRAPIIY. 


any electric disturbance independent of the wave-length. 
The reason for the rapid radiation is easily seen. The 
field of force is not concentrated as in the case of a Leyden 
jar between the two coatings, but stretches far into space 
between the top of the aerial and the earth. Moreover as 
the frequency is high there is very little time for the field 
to shrink to nothing before reversal takes place. 

(4) Drude has shown that, the less the damping of the 
transmitting circuit, the more nearly one fundamental wave 
is radiated. 

Aerial Loaded with Capacity .—The original Hertz oscil¬ 
lator had plates at each end to increase the capacity. The 
Lodge-Muirhead Syndicate have developed a system on 
these lines. Their aerial consists of two large carpets of 
wires, one high up in the air, the other formerly lying on 
the ground, but now preferably raised a few feet above the 
ground. This arrangement has several advantages over 
the single aerial wire:— 

(1) The vibrator has a larger oscillation constant giving 
a greater length of wave. 

(2) More energy can be stored with the larger capacity. 

(B) Consequently the resistance of the air-gap may be 

made smaller and the damping is diminished. 

(4) The energy is not radiated so quickly; this also 
reduces the damping. 

(5) The wave radiated is of more definite frequency than 
with the single aerial. 

The two principal variables are the size, and the height 



99 


of the aerial carpet above the earth carpet. The larger 
the carpet the less the damping and radiation; and the 
greater the syntony. The greater the distance the carpets 
are apart the longer the distance of transmission; but this 
is gained at the expense of syntony. 

Sir Oliver Lodge’s original plans have not yet been com¬ 
pletely carried out in practice. According to his ideas the 
transmitter would tahe the form shown in Fig. 62 instead 



Fig. 62. 


Fig. 63. 


of the practical form of Fig. 63. The difference between 
the two arrangements is one of symmetry. In the practical 
arrangement there is a mutual inductance between the 
wires A and B causing subsidiary waves, so that the 
resulting wave radiated cannot be made so pure as would 
otherwise be the case; but the great advance that has been 
made towards realising Lodge’s ideal may be gathered from 
the description of the latest developments described in 
Chapter XI. 

Coupled Systems .—At present the most usual method of 


h 2 


) > > 

















100 


RADIO-TELEGRAPHY. 


transmitting is that due to Braun, viz., coupling the closed 
Leyden jar circuit of Lodge to the open radiating circuit of 
Marconi. By increasing the capacity the closed circuit 
can, at the same time, be made to absorb as large a quantity 
of energy as required, and to contain the length of air-gap 
offering least resistance to the oscillatory discharge. As 
practically the only waste of energy is due to the small- 
resistance spark-gap, and that given to the coupled circuit, 
it is possible to set up a very powerful and slightly damped 
train of vibrations. 

The Radiating Circuit .—Connected to the closed oscilla¬ 
tory circuit is an open radiating circuit. The best method 
of connexion depends on the distance of transmission and 
the required absence of interference to other stations. 
With the radiating circuit, what has to be considered is the 
total amount of energy that is given it from the closed circuit 
during each oscillation, to be radiated, and this energy 
depends on the energy of the closed circuit and the method 
of coupling. With the closed circuit the damping is made 
small, but the radiating circuit has to radiate as rapidly as 
possible ; so the damping due to radiation should be large 
whilst the damping caused by resistance should be as 
small as possible. With only a small amount of energy 
given at each oscillation the single aerial may be used, 
omitting the spark-gap. With increased energy a greater 
radiating surface is necessary and multiple antennae 1 are 

1 The aerial wire is sometimes called an antenna on account of a 
supposed resemblance in action to the antenna of an insect. 

( i ( f 
< c 
* < c 

1 < r 


THE ELECTRIC OSCILLATOR 


101 


used. Different forms are employed in various systems. 
On ships parallel wires are generally placed a few feet apart 
(see Fig. 64), three or five of these being often used. One 
typical arrangement as used at the high power Marconi 
Station at Poldliu is shown in Fig. 65. 

Methods of Coupling .—Where oscillations in one circuit 
set up oscillations in an adjacent circuit the two circuits 



are said to be coupled. If a considerable portion of the 
field of force of the first circuit is embraced by the second 
the coupling is fast; if only a small portion, the coupling 
is loose. In Fig. 66 a circular loop of wire A is shown, in 
which an oscillatory current is growing. Another circular 
coil of wire, brought close to A into position B, embraces 
nearly the whole of the field and the coupling is fast; 
violent interaction takes place between the two sets of 
vibrations, which increases the damping in A. Moving the 

























































102 


RADIO-TELEGRAPHY. 



secondary coil to C, the field through it is lessened and the 
coupling is loose. In radio-telegraphy the circuit A may be 
taken as diagrammatic of the closed circuit, and the coils at 


aiiin Ul-t-' .- - 









































THE ELECTRIC OSCILLATOR. 


10:3 


B or C of the open radiating circuit. A greater total energy 
is transferred with coil at B, but a larger number of vibra¬ 



tions take place when it is moved to C. Two methods of 
coupling are employed, one electric and the other magnetic. 
The first method is shown diagrammatically 
in Figs. 67, 68, the second in Figs. 69, 70. 

It will be seen by the first there is actual 
contact between the two circuits ; in the 
second a portion of the magnetic field is 
common. In general it is the capacity 
effect that predominates in the closed cir¬ 
cuit, and the inductance in the radiating 
circuit. With the electric method the 
coupling is said to be fast or loose, depend¬ 
ing on whether a larger or smaller portion 
is common to both. Fig. 71 represents a fast, Fig. 68 a loose 
coupling. On the other hand the magnetic coupling can be 
made fast or loose by bringing the windings closer or further 






























104 


RADIO-TELEGRAPHY. 



G« 


-o D o 




C, 


E 


apart. The arrangement shown in Fig. 70 is the better 
than in Fig. 69, as both closed and aerial circuits are more 
symmetrical. Using the electric coupling, one of the latest 
methods of connexions as employed by the Amalgamated 

Radio-Telegraph Co. is 
shown in Fig. 72. The 
power circuit consists of 
alternator M, key T, 
choking coil R, and 
transformer P S. The 
primary oscillatory cir¬ 
cuit has condenser J, 
spark-gap I), and several 
windings of inductance 
which are also common 
to the aerial circuit. 
What is called an anchor 
spark Cf isolates the 
transmitting circuits 
during receiving, as may 
be seen by referring to 
Fig. 108. 

Damping of Vibrations 
in Radiating Circuit .—The variation of amplitude with 
the number of vibrations for a simple oscillatory circuit 
caused by the breakdown of the air-gap has been depicted 
in Fig. 17. When the disturbance in the radiating circuit 
is set up by the oscillations in another circuit the effect 


Mmmmc 


p 


R £ 


U 


E 




AnnMnnnr 


u 


E 


Eig. 72. 


[Reproduced from Electrical Engineering of 
Feb. 14tli, 1907, by permission of the Pro¬ 
prietors.] 
































THE ELECTRIC OSCILLATOR, 


105 


is somewhat different. In the case of a single radiating 
wire about 26 per cent, of the energy, given it by the 
first vibration of the closed circuit, is radiated. Now 
if the vibrations in the closed circuit were so rapidly 
damped that the energy given to the aerial during the 
second vibration were only 26 per cent, of that given in 
the first, then the amplitude of oscillation, in the radiating 
aerial for the second swing, would he the same as for the 
first swing. For the third vibration the energy would be 



83 per cent, of the second, after which the energy would 
diminish rapidly. But as explained, the damping of the 
closed circuit is made very much less than that of the open 
circuit; in fact it is feasible to make the amplitude of each 
vibration in this closed circuit 99 per cent, of the preceding 
one, so that the second vibration of the open circuit is 
173 per cent., and the third vibration 228 per cent, of the 
first. The amplitude increases until the energy given by 
the primary circuit balances the energy radiated by the 
secondary. Fig. 73 after Zeneck shows the amplitude of 






106 


RADIO-TELEGRAPHY. 


secondary vibrations with a closed circuit losing "1 per 
cent, of its energy each vibration, and in the same time the 
open circuit radiating 18 per cent. 

The Principal Wave of a Vibrating Circuit —With different 
musical instruments the same note gives different sounds 
due to harmonic vibrations, and in general the energy 
associated with these harmonics is very small. These 
harmonics have also been observed in the case of electrical 

vibrations, but there is 
another effect: with the 
electric oscillator there is 
not one fundamental vibra¬ 
tion, but the vibrations are 
such as if all the notes of 
a piano had been struck at 
once but with varying force. 
The vibration of the note 
struck loudest might aptly 
be called the principal 
vibration, and in the electric analogue the vibration 
associated with the greatest energy might also be called the 
principal vibration. Fig. 74 illustrates this. The horizontal 
scale gives the different wave-lengths, and the vertical 
height of the curve at any point is a measure of the energy 
of vibration for that particular wave-length, i.e the ordinates 
of the curve are a measure of the energy of vibration, the 
abscisses give the wave length. In Fig. 74 the principal 
wave is 600 metres. 














THE ELECTRIC OSCILLATOR 


107 


In the example given, the aerial radiates twice as much 
energy of 600 metres wave-length as what it radiates of 
either 500 or 750 metres wave-length. So if the station 
could just transmit signals over 1,000 miles to a properly 
tuned receiver, other stations within a limit of 250 miles 
tuned to receive at anything between 500 and 750 metres 
would be liable to be interfered with. If, however, the energy 
associated with the primary closed circuit be made of the 
order of 50 h.p. instead of, say, 5 h.p., the coupling 
between the closed and the radiating circuit can be made 
looser, so that the wave of 600 metres is associated with a 
500 metre wave of, say, only one tenth of the energy, and 
it is probable that stations further than ten miles would not 
be seriously disturbed. 

In an actual case measured by the author, the principal 
wave was 495 metres, the distance of transmission was 
60 miles, and signals were received by a ship 500 miles 
away. At a distance of 100 miles this ship would have 
found it necessary to use a wave length of less than 480 
metres or more than 520 metres to avoid interference 
or else employ a very loose coupling on the receiver, 
and use excessive power for sending. The method of 
finding the principal wave is described in the chapter on 
tuning. 

It is found that, the less the damping of the oscillator, 
the nearer the vibrations approach to a single fundamental 
one, so that with a very slightly damped circuit the vibra¬ 
tions might be likened to those caused by striking say the 


108 


RADIO-TELEGRAPHY. 


middle C of the piano with great force, the adjacent B and 
D with medium force, and the other notes so softly as not 
to be distinguishable. 

Limitations of Close Coupling .—At first sight it might 
appear to be advantageous to use as close a coupling as 
possible sending, if there were no outside stations in the 
neighbourhood, but this is not the case. Drude has 

theoretically shown, and 
the theory has been con¬ 
firmed by experiments 
by G. Pierce, that with 
the closest coupling 
theoretically possible the 
damping decrement is 
half the sum of the de¬ 
crements of the closed 
and aerial circuits. Thus, 
if the decrement of the 
aerial be 0*3 and that of 
the closed circuit 0'02, 
the combined decrement 
would be 0*16, so that the energy of each vibration cannot 
be made more than about 86 per cent, of the preceding one. 
He also showed that the weaker the coupling, that is, the 
less the energy that was transferred from the primary to 
the secondary circuit during each oscillation, the nearer 
the damping approached to that of the closed circuit. Also 
with very close coupling there is an interaction between the 


















THE ELECTRIC OSCILLATOR. 


109 


two circuits causing a compound wave, so that there are 
two maxima. 

Fig. 75 shows the relative energy of vibration in the 
radiation circuit, with A, coupling too close, B, coupling too 
loose, and C, coupling correct for sending maximum distance, 
D, possibly correct coupling for signalling a required distance, 
at the same time avoiding interference with an outside 
station. 

Coupled Circuits compared with Open Circuits .—The 
advantages of using coupled circuits as originally claimed 
by Braun are as follows :— 

(1) Larger amount of energy stored. 

(2) No danger from touching aerial wire. 

(8) Insulation of aerial wire not required to be so perfect. 

(4) Oscillations less damped. 

For short-distance working a large amount of energy is 
not required. For long distances, however, the battery of 
Leyden jars is a very convenient method of storing energy. 
The other method of obtaining a large capacity by means 
of a carpet aerial, as used by the Lodge-Muirhead Syndicate, 
is much more cumbersome. On the other hand, there is 
not the loss of energy due to coupling. Where this latter 
system is used between India and the Andaman Islands, a 
distance of about 300 miles, a 3 b.h.p. oil engine is used, 
and the carpet aerial is 10,000 square feet. For a 20 or 
50 h.p. station the area of the carpet would become exces¬ 
sive and troublesome if subjected to high winds. 

With the open circuit there is storage of energy in the 


110 


RADIO-TELEGRAPHY. 


aerial. Using the coupled circuit there is no such storage, 
and hence there is no danger from touching the aerial. 
With the open circuit the leakage is always taking place 
during the accumulation of energy; with the coupled 
system leakage only occurs during the time oscillations are 
taking place. 

For land stations the aerial can be easily protected, but 
for ships there is more liability to danger from using the 
open circuit. For extremely dry situations the question of 
insulation is not so important as for extremely damp 
tropical stations. 

In the case of closed circuits the oscillations can be made 
less damped by several methods:— 

(a) Reducing the resistance of the circuit by adding 
capacity, enabling a smaller spark-gap to be used. 

(b) Decreasing the coupling so that less energy is trans¬ 
ferred to the radiating circuit each vibration. 

(c) Making the closed circuit completely symmetrical. 

In the author’s opinion, up till lately this decreased 
damping is the principal advantage of using a coupled 
system. This is more especially of importance when inter¬ 
ference with any other station has to be avoided; it will, 
however, be seen from the chapter describing a Lodge- 
Muirhead station that very good syntony has now been 
obtained by making the circuits more nearly approach to 
Lodge’s original suggestions. 

It is probable there is another advantage, not originally 
claimed by Braun, due to the vibrations in the aerial circuit 


THE r ELECT RIO OSCILLATOR. 


Ill 


first rising to a maximum and then diminishing; this 
causes them to act with greater effect on a detector such as 



Fig. 76. 


would be placed in a sharply-tuned receiving circuit, which 
would require a cumulative wave of energy to actuate it. 



















112 


RADIO-TELEGRAPIIY. 


The Auto-Transformer .—This is the name given to a piece 
of apparatus for coupling two oscillatory circuits by direct 
electrical contact. It consists simply of a number of turns 
of wire, giving added inductance to the aerial circuit. A 
small portion of this inductance is made common to the 
closed circuit. If only one or two turns are common, the 
coupling is loose; with more and more turns in common, 
the coupling becomes closer. Loose and fast couplings are 
shown in Figs. 68 and 71. A combined auto-transformer, 
spark-gap, and battery of Leyden jars adjustable for 
radiating waves of from 120 to 1,000 metres, as used in 
the Telefunken system for ship work, is shown in Fig. 76. 

The Tesla Transformer. —The magnetic method of coupling 
is made by means of the high-frequency transformer first 
described by Tesla in 1891, when he used it for lighting by 
a single wire, and obtaining powerful brush discharges. It 
is made up of a few turns of wire in the closed circuit con¬ 
taining the spark-gap, and a larger number of comparatively 
thick wires surrounding the others in the aerial circuit. 
The principal points in designing a Tesla transformer are 
to obtain perfect insulation between the primary and 
secondary windings, to have no iron core, and for both 
windings to consist of a single layer of wires. 

The Auto and Tesla Transformer compared. — Both the 
electric and magnetic systems of coupling have their 
advocates. The auto-transformer has been mostly used by 
De Forest, and the Tesla transformer by Marconi; whilst the 
Germans use the electric method for long distances with close 


THE ELECTRIC OSCILLATOR. 


113 


coupling, and the magnetic method where loose coupling is 
necessary. The three first advantages for coupled systems, as 
given by Braun, are the same for both methods. Experiments 
made by G. Pierce would, however, tend to show that the 
magnetic method is the best. He found that after tuning send¬ 
ing and receiving circuits to the same principal wave, using 
the magnetic coupling, a change of wave in the sending circuit 
of from 2*j to 5 per cent, caused the energy received to be 
reduced to half; whereas, with the 
auto-transformer, the same reduc¬ 
tion of received energy was given 
by a wave-length 26 per cent, 
smaller, or 60 per cent, larger than 
the principal. These results do not 
appear so good as can be obtained 
with the carpet aerial. Pierce also 
found that under the best condi¬ 
tions and using the same power, 
the energy received with the auto-transformer was only 
1% times as great as with the electro-magnetic coupling. It 
must, however, be borne in mind that these experiments 
were carried out over distances of a few hundred feet. 

Couplings for High Power Stations .—In the last chapter, 
Fleming’s method of radiating considerable horse-power 
was described, and it was shown how by modifications in 
the low-frequency generating apparatus he was enabled to 
produce 20,000 trains of waves per second instead of several 
hundred. Braun attacked the problem differently. He 



U.T. 


I 









114 


BADIO-TELEGKAPHY. 


arranged his closed circuit as in Fig. 77, where Ii I 2 are 
leads from a transformer to three spark-gaps Gi G 2 G 3 , and 
charging three condensers Ki Iv 2 Iv 3 in parallel. During 
the oscillatory discharge the three spark-gaps, condensers 
and inductances Li L 2 L 3 of the Tesla transformers are in 
series, so that throughout the discharge, the capacity of the 
circuit is one third and the inductance three times as great 
as it is during the charge. It would appear that the object 
of this arrangement is to enable the use of three times the 
total length of spark-gap with one third of the strain on 
the condensers. 

Another method used by Braun has been to use multiple 
aerials with separate closed circuits for each aerial, the 
spark-gaps being cross-connected by high resistance coils, 
and the self-inductances cross-connected by inductionless 
wires to insure that the two circuits should vibrate in 
phase. 

System of Directed Waves by means of Horizontal Wires .— 
In many cases it would be very advantageous to radiate 
waves in only one direction, and sometimes it would be 
equally advantageous to receive signals from only one 
place. Marconi has developed an arrangement first used 
by Garcia. 

Instead of using vertical wires, Marconi has used long 
horizontal wires above the earth, as depicted in Fig. 78, 
where A is a station connected for sending, with B for receiv¬ 
ing. As will be seen, the wires at each place are arranged 
to lie in the same direction with connections at the nearest 


THE ELECTRIC OSCILLATOR, 


115 


points to the stations. He has found that the horizontal 
length should he great in proportion to the height of wire 
above the ground, but for high power stations this may be 
100 feet or more; the wave-length should be large, and the 
best results could be obtained by open circuit working. With 
this arrangement, although the radiation is a maximum in 
one direction, considerable energy may be radiated in other 
directions. In one of Marconi’s experiments, signalling over 
a few hundred metres, when the horizontal wires were at 
right angles to each other, 



the received current was 


reduced to about one half, HU 

and when the two wires 

pointed in same direc- 1 





E 


Fig. 78. 


tion the received current was about two thirds of the 
maximum. 

Probably the most interesting result so far obtained is 
that a land station was found able to determine the bearing 
of a ship, signalling with the horizontal wire. 

There is no doubt that nothing could be simpler than 
this arrangement; but, at the same time, for long distance 
working it is probable that the length of horizontal wire, and 
consequently the space required for the station, would have 
to be considerable. 

Braun s System of Directed Waves .—Braun has been 
working for many years on this subject, but his system has 
not yet advanced beyond the experimental stage, so it is not 
proposed to describe it here in any detail. The radiation 


i 2 











116 


RADIO-TELEGRAPHY. 


is more concentrated in one direction than with the Marconi 
arrangement, but on account of its complexity it is probable 
that it will always require considerable skill to work. 
Briefly it consists in using three vertical oscillators at the 
corners of an equilateral triangle, and producing oscillations 
in each, differing in phase by a definite amount. By this 


Aerial 



Fig. 79. 

[Reproduced from Electrical Engineering of Nov. 14th, 1907, by permission of 

the Proprietors.] 

means Braun has radiated about thirty times more energy 
in the maximum than in the minimum direction. At the 
receiving end Braun uses a wire not quite horizontal, but 
sloping slightly towards the incoming wave. 

The Directive System of Bellini and Tosi. —Marconi’s 
directive system is only a special form based on a general 
principle, namely, that any closed oscillator placed in a 






THE ELECTRIC OSCILLATOR. 


117 


vertical plane radiates more strongly in the horizontal 
direction of that plane than in any other direction. E. 
Bellini and A. Tosi have been experimenting with various 
forms of closed oscillator circuits between Dieppe, Havre 
and Barfleur for both sending and receiving, and their 
system has lately been described in Electrical Engineering. 



[Reproduced from Electrical Engineering of Nov. 14th, 1907, by permission of 

the Proprietors.] 

The general form used has been a triangle with one side 
parallel with the ground and the apex open. Bather more 
power is required than with a non-directive system, but 
in no case was more than 500 watts used for signalling the 
106 miles and the directiveness of the signals was well 
marked. To vary the direction of sending or receiving two 
aerial triangles with bases A B, Ai Bi, Fig. 80, at right 
angles have to be erected. For direct excitation the aerial 












118 


RADIO-TELEGRAPHY. 


circuits are connected to a continuous spiral as shown in 
Fig. 79 the point of connection being varied to give the 
desired direction to the radiation. For inductive sending, 
two secondaries of a transformer each have their planes in 
those of one of the triangles, whilst the primary can be 
rotated; and in the same way for inductive receiving the 
primaries M N, Fig. 80, are fixed, and the secondary S is 
moveable. As the first patent only dates from April, 1907, 
it is probable considerable improvements remain to be 
worked out. 


CHAPTER VII. 


THE ELECTRIC OSCILLATOR—PRACTICAL DETAILS. 

The Aerud .—The ohmic resistance must be kept as low 
as possible, whilst the insulation resistance and capacity 
must be as high as possible. With oscillating currents it 
has to be remembered that it is only the outside skin of 



the conductor that is effective, so that it is surface, not 
mass, that has to be aimed at. Insulation is especially 
important with open circuit sending, as the leakage in the 
aerial takes place during the comparatively long time of 
charging. The oscillatory current will also tend to partly 
follow the path of leakage, so that a small leak quickly 
develops into a large one. The author has found with 
open circuit sending that highly vitrified porcelain is the 
























120 


RADIO-TELEGRAPHY. 


only insulator that has any practical value in the vibrating 
circuit. He has used the type of insulator shown in 
Fig. 81 with great success at the mast head. Where the 
aerial wires enter the building a long porcelain tube slightly 
sloping down to the outside is satisfactory. 

Bare wire is generally used, 
though well insulated wire has 
its advantage in preventing 
dissipation of the energy during 
charge by convection. The 
difficulty is to keep the insula¬ 
tion in good order under the 
conditions, and in the places 
where radio-telegraph stations 
are erected. 

Copper is the best material 
for the aerial, and it is best to 
have the copper tinned. The 
author, when this precaution 
was not adopted, has found that 
in a salt atmosphere a chloride 

[Reproduced from Electrical Engineer- of COpper Was Very rapidly 
ing of Feb. ]4th, 1907, by permission 

of the Proprietors.] formed, which was probably 

due to electrical discharges from the conductor. 

It is also important that there should be no sharp points 
which would cause loss from brush discharges. 

As an illustration of the latest type of aerial construction 
for a small power station, that erected in 1906 by the Post 
















THE ELECTRIC OSCILLATOR 


121 



Fig. 83. 

[Reproduced from Electrical Engineering of Feb. 14th, 1907, by permission of 

the Proprietors.] 


Office may be taken as a good example. The contractors 
were the Amalgamated Radio-Telegraph Co., the system 























122 


BADIO-TELEGKAPHY. 


employed being that of De Forest and Maskelyne. Figs. 82 
and 83 show the general arrangement of the wires diagram- 
matically and by photograph. The construction has been 
well described in Electrical Engineering as follows:— 
“ The masts that carry the air-wire system are 122 feet 
high, and are of very noteworthy construction. Each has 
been built (in a horizontal position) out of deal planks 
treated with carbolinium. A start was made by placing 
together five planks of lengths varying from 5 to 25 feet; 
to this stump other 25 feet planks were laid in continuation, 
and the process continued, with proper tapering, till the 
whole mast length is formed without tw T o butt joints ever 
coming together. The whole is bolted up by bolts at every 
18 inches. The lower part of the mast is cased round with 
four planks, but the upper part is planked only where the 
edges show. The masts being only 1 foot square at the 
base, prove very pliable in high winds, yet exceedingly 
strong. Each mast is steeped in concrete, and has three 
sets of four stays, which are tied to ground anchors con¬ 
sisting of long bolts through 6 feet oak baulks buried 6 feet. 
The stays are not continuous wire rope, hut are each broken 
into short lengths by 3 feet lengths of pickled ash, furnished 
with iron eyes. The air-wire system consists of six equal 
wires hanging from a yard and spreader of oak. Eighteen 
inches from the top they are electrically connected by a 
cross wire. The wires at both stations dip at about 30 
degrees from the vertical towards the north-east, and are 
held apart hy insulated stays near the bottom. Here they are 


THE ELECTRIC OSCILLATOR. 


123 


gathered into two bunches of three, and both bunches are 
insulated and led through an ebonite tube into the apparatus- 
room.” As a further example, an illustration of the aerial at 
Scheveningen (Fig. 84) on the Telefunken system is given. 

For large power stations steel construction is often used. 



Fig. 84. 


Typical examples are the Marconi aerial at Poldhu (Fig. 85) 
and the Telefunken aerial at Nauen (Fig. 158). 

The Lodge-Muirhead insulator for leading aerial wires 
into a building is shown in Fig. 86. 

Earthing the Aerial .—In the earliest days of radio¬ 
telegraphy it would appear probable that one of the most 














124 


RADIO-TELEGRAPHY, 



Fig. 85 










































THE ELECTRIC OSCILLATOR. 


125 


frequent causes of failure in the case of land stations was 
due to defective earthing arrangements. The plan adopted 
was to imitate as closely as possible the earthing arrange¬ 
ments used in telegraphy, that is, to use large pieces of 
copper buried in the ground. By this means a good 
metallic connexion could be obtained, but this is not all 



that is required. From the elementary theory the reader 
will notice that it is important the closed lines of force from 
the aerial should stretch out well into space. If the earth 
is an especially bad conductor in the neighbourhood of 
the aerial the greater part of the field of force will be con¬ 
centrated on the earth connecting wire, so that the 
radiation each period is small. In the case of the early 




126 


RADIO-TELEGRAPHY. 


stations the resistance of the oscillating circuit was high, the 
damping large, and, moreover, the receiving arrangements 
were such that they were only effective when the initial 
radiation during the first discharge was great. The sea being 
a comparatively good conductor, sending from ship to ship 
has always been comparatively easy, and the greatest diffi¬ 
culty has always been experienced over sandy deserts. For 
high power land stations the problem of earthing is most 
important; Marconi and Fessenden bury copper wires, 
which spread out from the radiating station for the distance 
of a mile or more. 

Another loss occurs using a conducting earth, as con¬ 
siderable dissipation of energy takes place where the earthing 
wires enter the earth, the current flowing through varying 
paths of high resistance. With small power, and the 
surface of the earth a fairly good conductor, the author is 
doubtful if any of the current reaches a buried plate. This 
loss is probably greatest with open circuit working, but it 
always occurs as shown both by the experiments of Lieut. 
Evans with open circuits, and of Duddell and Taylor with 
coupled circuits. In a special case, using the open circuit 
system, Lieut. Evans found the oscillatory current was 
reduced 56 per cent, when the lower capacity area of Lodge 
was allowed to touch the ground, and it was reduced 85 per 
cent, when this capacity area was connected to a telegraphic 
earth. Using the same system, and the capacity area 
lying on the ground, the author has noticed sparking from 
the radiating wires to the ground. 


THE ELECTRIC OSCILLATOR. 


127 


Messrs. Duddell and Taylor, using a coupled system in 
their Bushey Park experiments, earthed the aerial by means 
of 75 feet of wire netting lying on the grass. They found 
by using a metallic earth the received current was only 60 
per cent, of that obtained by the wire netting. 

These experiments show that for land stations the 
inductive earth with earthing wires forming one plate of 
a condenser 1 is better than the old telegraphic conducting 
earth. This inductive earth is used both by the Lodge- 
Muirhead Syndicate and in the Telefunken system. 

The author is of opinion that the ideal earthing would be 
a combination of the lower insulated capacity area of Lodge 
with underneath it the radiating earthed wires of Marconi, 
but he is not aware that this has ever been tried. 

In the case of a ship circuit, however, the metallic earth 
may be made good, without loss, by taking well insulated 
wires to the steel framework of the vessel. 

Protection from Lightning .—In the case of land stations 
the aerial is practically a lightning conductor entering a 
building ; for this reason every precaution should be taken, 
and it is unadvisable to attempt to work a radio-telegraph 
station during a bad thunderstorm. Long-break highly 
insulated switches should be placed where the aerial enters 
the building, and the author has used in addition the device 
shown in Fig. 87. The earthed copper rod A, lying in a 
wooden frame hinged at B, rests on the ground under 
normal conditions, but during a thunderstorm it can be 

1 See Fig. 63. 


128 


RADIO-TELEGRAPHY. 


raised by means of a rope from the signalling room so as to 
make contact with the aerial. 

With the De Forest system there is a small spark-gap 
from aerial to earth called an anchor-spark, which acts as 
a partial protection against lightning. 

Variation of Effective Spark-Length with Capacity .—To 
obtain a good oscillatory discharge in a circuit with little 



damping, it is necessary to make the resistance as small as 
possible. The greatest part of the resistance is in the 
spark-gap , 1 so this should be short. On the other hand, 
the longer the distance of transmission the more the energy 
that is required to be stored before oscillations take place. 
The energy stored varies with the capacity of the circuit 
and the square of the difference of potential to which the 
arms of the oscillator are raised. This difference of 

1 The resistance referred to is that during the oscillations. 









THE ELECTRIC OSCILLATOR. 


129 


potential is mainly determined by the length of the spark- 
gap, therefore the longer the gap the greater is the 
amount of energy that can be stored, but under most 
circumstances this can only be done by decrease of 
efficiency; at the same time it is found that for a given 
spark-gap the greater the energy that can be stored, the 
less is the resistance. It is the most important problem 
at the transmitting station to store as much energy as 
possible in the aerial, and, at the same time, reduce the 
losses in the spark-gap. The desired result has to be 
sought by increasing the capacity of the circuit, as this 
has the twofold effect of increasing the energy stored and at 
the same time allowing a longer spark-gap to be used for the 
same loss of energy. It is found in practice that, for a given 
oscillatory circuit and a given amount of energy stored for 
each group of surgings, there is a spark-length that is 
best. If the energy be sufficient, the greater the capacity 
the longer is the best spark-length, and below a certain length 
of gap arcing takes place. If, however, the energy supplied 
be too small for the capacity the potential may not even be 
raised sufficiently for the disruptive discharge to take place. 

Under a given set of conditions the best spark-gap can 
only be found by placing an ammeter in the oscillatory 
circuit preferably at the antinode of current, and trying 
different lengths of gap till the largest reading on the 
instrument is obtained; or the ammeter may be placed in 
a subsidiary circuit acted on inductively and having the 
same oscillation constant. 


R.T. 


K 


130 


BADIO-TELEGBAPHY. 


In Figs. 88 and 89 are shown the results of experiments 
made by Rempp to show the relation between spark-length, 
capacity of oscillatory circuit, and spark resistance, with 
zinc spark-knobs one and a half centimetres in diameter. 
It will be noticed that for a given capacity the resistance 
of the spark is a minimum for a given length, increasing 
for both shorter and longer gaps ; also if the capacity is 

below a certain critical 
value, the rate of increase 
of resistance with spark- 
length is very rapid. 
Rempp calculated the 
damping decrements from 
the results shown in Fig. 
90, and found that with 
each capacity the [lowest 
decrement was of the 
order 0*07 to 0*08, rising 
as a rule to about 0*15 for sparks of either 0’1 or 5 centi¬ 
metres. 

Characteristics of the Oscillatory Spark .—The best spark 
can only be found by means of a hot wire ammeter, as 
before described, hut it is easy to distinguish an oscillatory 
spark from one which is not. The ordinary spark of an 
induction coil working with small or no capacity across the 
terminals is blue, thin and jagged when the gap is long, 
and red and furry when very short. On the other hand, 
the oscillatory spark is thick, white, and, under the best 



Capacity in jm 1 . 1 ! Microfarad. 
Curve A Spark Gaps = 2 cm. 
.. B „ —5 cm. 


Fig. 88. 
















THE ELECTRIC OSCILLATOR. 


131 

conditions, straight, with a much more intense sound, which 
is quite deafening when large quantities of energy are being 
utilised. The sound of the oscillatory spark has generally 
been described as of a snappy nature, but Sir Oliver Lodge 
has lately pointed out that this snappy spark only occurs 
with rapidly damped oscil¬ 
lations. An induction coil 
made for wireless tele¬ 
graphy that would give a 
twelve inch non-oscillatory 
spark, would also give a 
good oscillatory spark of 
about quarter of an inch 
when used in a circuit 
having a capacity of one 
hundredth of a microfarad. 

Potential Difference re¬ 
quired to Produce a Disrup¬ 
tive Discharge .—It is much 
easier to obtain a disruptive 
discharge between points 
than between knobs, and 
the larger the radius of curvature of the knobs the greater will 
be the potential difference required. In wireless telegraphy 
as it is the object to store as much energy as possible before 
the disruptive discharge takes place, the potential difference 
must be made as great as possible, hence it has generally 
been found unsatisfactory to use points. On the other 

k 2 



0 1 2 3 4 5 

Spark Length in Centimetres. 


Curve A 

Capacity = 0 000273 

„ B 

„ = 0 000435 

„ c 

„ = 0000853 

,, D 

„ = 0-00109 

.. E 

= 0 00303 

„ F 

„ = 000686 


Fig. 89. 























132 


RADIO-TELEGRAPHY. 


hand, Rempp in his experiments found that under the best 
conditions of spark-length the damping decrement was the 

same for knobs from 1*5 



1 2 3 

Spark Length in Centimetres. 

Curve A Diameter of Spark Knobs = 5 cm. 

ti D ft ,, tz 3 ft 

M ^ ft »» = J'P it 



0-2 -4 -6 -8 1 1-2 1-4 1-6 

Sparking distance in Centmetres. 
Curve A Radius of Spark knobs 2-3 cm. 
„ B „ „ 10 „ 

m ^ rt m 0‘S tr 

m D ft tf 0-25 i. 


Eig. 91. 


to 5 centimetres diameter 
(Fig. 90), but with longer 
spark-gaps the decre¬ 
ment was increased by 
using the larger knobs. 
It is thus evident that 
for a given set of con¬ 
ditions there is a suit¬ 
able size for the knobs 
to be made. 

To keep the surface 
of the spark knobs free 
from points these are 
usually kept polished. 
With the induction coil 
a much greater storage 
of energy can be obtained 
with the knobs polished. 
This effect was the most 
marked with the original 
Hertz oscillator; as the 
energy stored was very 
small relatively to the 
length and resistance of 
the gap, it was found 


































THE ELECTRIC OSCILLATOR. 


133 


best to repolish the knobs after every few minutes. On the 
other hand, with an alternator which has a flat curve of 
E. M. F. (Fig. 55), the maximum potential difference 
between the arms can be made so much smaller that clean¬ 
ing the knobs is of no advantage. Lodge claims that under 
the best conditions a series of 
points in ionised air may be 

. ... 90,000 

employed so as to maintain 
a lower resistance of the gap 60000 
for a longer period. 70,000 

For obtaining the first dis- - 60000 
ruptive discharge the varia- 

x 50,000 

tion of sparking distance 
with volts for different sized 
knobs up to F5 centimetres 
spark-gap, according to A. 

Heydweiller, is given in 
Fig. 91, and for longer gaps, according to J. Algermissen, 
in Fig. 92. 

Multiple Spark-Knobs .—In some of the earliest experi¬ 
ments made by Lodge and Righi, and in the earliest 
experiments of Marconi, the single spark-gap of Hertz was 
replaced by several gaps in series, but single sparks were 
again used by ah the Wireless Telegraph Companies till 
1904, when Slaby found that small gaps had propor¬ 
tionally greater conductivity than large gaps. He replaced 
one gap of 10 millimetres by three gaps of 2 | milli¬ 
metres. The discharge pressure in each case was 30,000 



>2 3 4 5 6 

Curve A Radius of Spark Knobs 2-5 cm. 
B 10 


Fig. 92. 














m 


RADIO-TELEGRAPHY. 


volts, but whereas the single spark had a resistance of 
15 ohms, the total resistance of the three gaps was 0*6 ohm. 
It may be noted that the total energy stored before dis¬ 
charge was the same in each Case, and that the increased 
efficiency was partly due to the use of a smaller total 
length of gap, this being 7*5 millimetres against 10 milli- 



Eig. 93. 


metres for the single spark. It would, therefore, appear 
that the multiple gap is best for two reasons:— 

(1) Reduction of total gap for the same energy stored in 
aerial. 

(2) Reduction of ohmic resistance for the same total 
length of spark-gap. 

Like other factors in wireless telegraphy the best number 
of gaps and length can only be found by experiment for 
given conditions. Multiple spark-gaps have now been used 
for some time in the Lodge-Muirhead and Telefunken 









THE ELECTRIC OSCILLATOR. 


135 


systems, one type of the last named being illustrated in 
Fig. 98. 

Material of Spark-Knobs and Density of Dielectric .—The 
resistance of the spark-gap also depends on the material of 
which the knobs are made. A comparison between iron 
and brass or zinc knobs, according to Fleming, is given in 
Fig. 94. 

The Rev. Jervis-Smith found in 1902 that the use of 
compressed air round the 
spark-gap checked leakage, 
enabling the oscillatory 
circuit to be charged to 
a higher potential. Fessen¬ 
den later has employed 
compressed air with both 
spark-gap and condensers 
for the same purpose. 

Position of Spark-Gap .— 

There are two sources of 
annoyance from the oscil¬ 
latory spark, the sound and the ozone 1 given off. On 
account of these causes it is advisable, when practicable, to 
place the spark-gap in a separate room from the operator, 
and with it may be conveniently placed the sending trans¬ 
former, inductance and Leyden jars. In some systems the 
gap is enclosed in a case to deaden the sound. In the De 

i Ozone is a modified form of oxygen which, besides having a 
disagreeable smell, is liable in sufficient quantity to cause headache. 



Curve A Radius of Spark knobs 2-5 cm. 


B 


10 


Fig. 94. 















136 


RADIO-TELEGRAPHY. 


Forest system the winding of the auto-transformer surrounds 
this case, forming a very compact arrangement. In the 
Telefunken system the case is covered with felt. 

Arcing .—It has already been pointed out how an induc¬ 
tion coil has to be adjusted to obviate trouble from arcing. 
When it occurs the whole or most of the energy is dissi¬ 
pated as heat in one direction. It is due to the air-gap 
breaking down whilst the aerial is still being charged. 
This breakdown should occur at the same time as the 
potential difference of the alternator becomes a maximum, 
or at the break of the hammer of the induction coil. When 
the arc is predominant the spark becomes red, furry and 
hissing. The best remedy is to reduce the charge given to 
the aerial by decreasing the current through the primary 
of the alternator, or weakening the tension of the spring of 
the induction coil. Increasing the spark-length decreases 
the arc, but increases the resistance, so it is not generally 
practicable. Keeping the knobs clean and using larger 
knobs is occasionally useful, and using multiple spark- 
gaps greatly reduces troubles from arcing. It must be 
remembered the primary cause of the trouble is that the 
capacity to be charged is too small for the apparatus 
charging it. 

Coupled Circuits .—To obtain the best results with coupled 
systems the two most important factors are a symmetrical 
arrangement of the closed circuit, and a suitable co-efficient 
of coupling between the closed and open circuits. To 
obtain symmetry two sets of condensers in series have to be 


THE ELECTRIC OSCILLATOR. 


137 


used; the best coupling varies with the conditions of 
working. Perhaps one of the greatest advantages of using 
the auto over the Tesla transformer lies in the ease of alter¬ 
ing the inductance, so that the best coupling*can be found 
by experiment on the spot. The coupling between two cir¬ 
cuits may be defined as the mutual induction of the two 
circuits divided by the square root of the product of the self¬ 
inductance of each circuit. The greater the mutual induc¬ 
tance the closer is the coupling. According to Zenneck it is 
never advisable to have a much closer coupling than 0*8. 
When the coupling is adjustable, it is most important to have 
good electrical contact and an easy means of altering the 
position of the contact. One method is to tap the auto¬ 
transformer at each turn, connecting to a series of plug 
terminals; another method is to use a clip that can be 
fastened direct to the transformer winding. Either of these 
arrangements may also be used for short circuiting coils of 
the sending inductance not required in circuit. The con¬ 
denser generally adopted is the Leyden jar, batteries of 
these jars being formed, each jar having a capacity of about 
O'OOl microfarad. In the Telefunken system the jars are 
replaced by long glass tubes of small diameter, giving greater 
capacity for the same weight of material. Eig. 95 illus¬ 
trates the framework of a condenser-battery for a 600 mile 
station. 

Transmitting Key .—Much greater difficulty is experi¬ 
enced with the transmitting key than in telegraphic work on 
account of the larger currents to be broken; and massive 


138 


RADIO-TELEGRAPHY 



Fig. 95. 
























THE ELECTRIC OSCILLATOR. 


139 


platinum contacts have to be used, the break being shunted 
by a condenser. The Marconi Company employ a type of 
key for small power stations with the condenser in a case 
below. They use a relay for alter¬ 
nating currents of 20 amperes 
or more, and the break is ar¬ 
ranged to take place at zero 
current to prevent sparking at 
the contacts. 

In the Telefunken system the spark between the contacts 
A C (Figs. 96 and 97) is extinguished by an electro¬ 
magnet W. For larger power automatic minimum current 




















140 


RADIO-TELEGRAPHY. 


cut-outs are used, and when 40 amperes or more has to be 
broken, several contacts are arranged in multiple. 

Auto-Transmitter .—In certain cases, when quick signalling 
is required, it is necessary to obtain accurate spacing of the 
tape-received signals, and it is advisable to use an auto¬ 



transmitter. A tape is first punched in a special punching 
machine, and then passed through the auto-transmitter, 
which automatically makes and breaks the primary of the 
transformer circuit. The auto-transmitter supplied by the 
Lodge-Muirhead Syndicate is shown in Fig. 98 and the 
diagram of connexions in Fig. 99. 







































































THE i ELECTRIC OSCILLATOR. 


141 


Arrangement of Apparatus .—For a small power station, 
such as at Skegness, where the alternator gives nine amperes 
at 110 volts, probably the arrangement of the apparatus in the 
oscillatory circuit, adopted in the De Forest system, is the 
best. The battery of Leyden jars is shown at the far end 


CPARK COIL 



of the table in Fig. 100. On this is placed the auto-trans¬ 
former ; this embraces the spark-gap, which is enclosed in 
a talc casing. At the top of all may be seen the handle for 
adjusting the spark, which can be regulated from £ to 2 inches. 
The rest of the table is taken up with receiving apparatus. 

The Poulsen Arc .—The arrangement of the oscillatory 
































































142 


RADIO-TELEGRAPHY. 



circuits is the same as with other systems, the actual 
arrangement of the station at Lyngby being given in 
Fig. 101, the arc only taking the place of the spark; but a 


Fig. 100. 

[Reproduced from Electrical Engineering of Feb. 14th, 1907, by permission of the 

Proprietors. ] 

large number of practical details require special considera¬ 
tion. The most important factors appear to be to keep the 
electrodes of the arc cool, and to keep the length and 

















THE ELECTRIC OSCILLATOR. 


143 


current through it constant. It is supposed that the good 
results, obtained by using hydrogen, are due to its greater 
heat conductivity. Oxygen is prejudicial owing to combus¬ 
tion and consequent heating of the electrodes. To keep 
these cooler it is advantageous to use a copper anode, and 
with large currents to artificially cool the anode. 

To keep the arc constant 
Poulsen employed at first for 
the cathode a carbon of large 
diameter, revolving at a cir¬ 
cumferential speed of about 

mm. per second. Addi¬ 
tional carbon was formed on 
the end, which was cut off 
as it revolved, or else the 
carbon was changed at the 
end of a revolution. In his latest apparatus, however, he 
makes the arc revolve round the edge of the carbon. 
Ordinary illuminating gas ma} T be used, but it must be 
continuously changed, due to the action of the oscillatory 
currents. The arc is kept in position by a transverse 
magnetic field, the electro-magnet also acting as a choking 
coil in the main circuit as shown in Fig. 101. 

Poulsen has patented a large number of methods of 
signalling to take the place of the ordinary transmitting 
key to break the main current. Amongst these may be 
mentioned the following :— 

(1) Short circuiting a resistance in the generator circuit. 






A/VV^AM 


Fig. 101. 





















144 


RADIO-TELEGRAPHY. 


(2) Short circuiting a resistance in the antenna circuit, 

(3) Making and breaking the arc. 

(4) Altering the length of the arc. 

(5) Altering strength of transverse magnetic field. 

(6) Altering the gas flow through the arc. 

Marconi's Transatlantic Practice .—Marconi now uses at 
Poldhu a high-tension continuous current, which supplies 
two circuits containing capacity and inductance. A third 
oscillatory circuit is brought into alternate proximity by 
means of a rapidly rotating disc nearing two balls in the 
first-named circuits. Alternate sparks from these balls to 
the disc produce the necessary oscillations in the third 
circuit, from which the energy is fed to the aerial. The 
aerials at Clifden and Glace Bay consist of 200 wires 
extending 1,000 ft. at a height of 180 ft. from the earth 
giving a partially directional character to the radiation. 
The wave-length is 4,000 metres; the sending capacity is 
1*8 m.f. made of air condensers, and the spark-length is 
three-quarters of an inch. 


CHAPTER VIII. 


THE RECEIVER-METHODS OF ARRANGEMENT. 

History .—The first improvement from the original Hertz 
loop of wire, broken by a minute spark gap, was the use of 
a number of filings. Branly had found in 1890 that a tube 
of filings could be made, which was completely non-conduct¬ 
ing under ordinary conditions, but that with such a tube a 
small difference of potential between the ends, as would be 
produced by an electro-magnetic wave, caused the string 
of filings to become a conductor to an electric current. 
If the current ceased the tube would still remain a conductor 
till it received a tap, when it became again a non-conductor. 
Lodge called this tube of filings a coherer, and he improved 
the circuit in 1894, by using a relay with arrangements for 
recording signals and tapping the coherer at the same time. 
Popoff, in 1895, made his receiving circuit a single wire 
stretching high up into the air, and Lodge and Marconi, in 
1898, placed the coherer in a secondary circuit at an anti¬ 
node of potential instead of near the node, which had 
formerly been the only convenient place to fix it. Since 
1898 a large number of improvements have been made in 
detail, making the circuits vibrate more to one particular 
frequency and less to various other waves; and numerous 

R.T. L 


146 


RADIO-TELEGRAPHY. 


forms of detectors have been invented which are considerably 
more sensitive and reliable than Branly’s coherer. Con¬ 
siderable progress may be expected in the near future as 
regards the problem of receiving signals from one definite 
direction. Garcia, in 1900, 1 showed that by laying the 
receiving wire horizontally on or above the ground, the 
electric vibrations are much stronger when the direction of 


V 



the wire is away from the sending station. Bellini and 

Tosi in 1907 have also received directive 
signals by using two closed aerial circuits 
in a vertical plane and at right angles to 
each other. 

Method of Receiving Radio-telegrapliic 
Signals .—It has been pointed out that when 
an electro-magnetic wave strikes a conductor 
surgings of electricity are set up. As in the 
Fig. 102 . case of the transmitter, at one moment the 
whole of the energy is potential, with a node at earth and an 
antinode at the top of the aerial, whilst after a quarter of a 
period the energy is all kinetic, with a node at the top of the 
aerial and an antinode at earth. To detect electric oscilla¬ 
tions in a receiving aerial a sufficiently sensitive instrument 
for detecting small differences of potential must be inserted 
at the antinode of potential, or an instrument for detecting 
minute rapidly-alternating currents must be placed at an 
antinode of current. Most detectors are not sufficiently 


1 The directive methods of receiving were described in Chapter VI., 
as these are based on the same principles as directive sending. 













THE RECEIVER—METHODS OF ARRANGEMENT. 147 


V 




sensitive to be used direct for recording or reading signals; 
they are usually shunted by a circuit with a battery in which 
is placed a relay or a telephone. The change of the electric 
propei ties of the detector causes in general a current or 
more current to pass through the local circuit, working the 
relay in the one case or making a click in the telephone in 
the other case. Fig. 102 represents the simplest form of 
receiving circuit. The current detector A is placed at an 
antinode and is shunted by a Le- 
clanche cell B, and a telephone re¬ 
ceiver C. Under ordinary conditions 
there is a minute steady current 
from the cell through the detector 
and telephone. An electric oscilla¬ 
tion in the aerial alters the proper¬ 
ties of the detector, so that the 
resistance is greater or less thereby, Fig. 103. 

decreasing or increasing the current in the receiver, causing 
clicks, whilst waves are being transmitted from the sending- 
station. When the waves cease, the detector and circuit 
assume, or are made mechanically to assume, their normal 
condition. 

The Receiving Transformer .—At first only potential dif¬ 
ference detectors were used in wireless telegraphy, and they 
were placed in the least sensitive position. Lodge and 
Marconi overcame this difficulty by the use of a special 
transformer which enabled the detector to be placed at the 
antinode. Fig. 103 shows the arrangement. The aerial A is 











148 


RADIO-TELEGRAPHY. 



connected through the primary C of the transformer to a 
wire B leading to the earth, or earth capacity. The 
secondary D of the transformer, with antinodes of potential 
at F and H, is connected to the coherer G, which is an 
insulator to direct currents under normal conditions, but 

becomes a conductor 
when there is sufficient 
difference of potential 
across it such as may 
be caused by a wave 
striking the aerial. As 
the coherer G has a 
very minute and variable 
capacity, it is generally 
shunted by a larger 
variable capacity K, to 
enable the secondary 
circuit to be brought 
into accurate tune—that 
is, to have the same 
oscillation constant—as 
the aerial circuit. 


Fig. 104. 


Fig. 104 illustrates the transformer used in the Telefunken 
system for receiving with loose coupling. It will be noticed 
the winding of the primary is removed from the secondary, 
and it can be shifted so that the windings do not surround 
those of the secondary. 1 Marconi sometimes places a 
1 Other types of receiving transformers appear on pp. 222, 237. 














THE RECEIVER—METHODS OF ARRANGEMENT. 149 


condenser at the node of potential to which the Morse 
inker or telephone circuits are connected. 

Low resistance current detectors are always placed at the 
antinode of current, with a condenser at the node. Such 
an arrangement for diplex receiving is shown in Fig. 105. 
The circuit A with condenser in series with the aerial picks 
up short waves, whilst the circuit B with inductance in series 




with the aerial is tuned to receive the longer waves. The 
wires C go to the local batteries and telephones. 

Auto-Transformer .—Another method due to Professor 
Slaby is sometimes used. It will be seen from Fig. 106 
that the device acts on a similar principle to the sending 
auto-transformer. The aerial A is connected through 
an inductance B, which is common to a secondary circuit, 
containing an additional inductance C and coherer D, which 
is shunted by a variable condenser. The one shown in 
Fig. 107 is for receiving waves of from 600 to 6,000 metres. 





















150 


RADIO-TELEGRAPHY. 


Importance oj Syntony .—When an electro-magnetic wave 
is radiated from a wireless telegraph transmitter, not only 
waves of one definite frequency are produced, but a large 



Eig. 107. 

number of other waves, which may be associated with 
nearly as much energy as the principal one. As in the 
sending station, the problem is to radiate as far as possible 
waves approaching to one frequency, so at the receiving 















THE RECEIVER—METHODS OF ARRANGEMENT. 151 


station the object is to make the detector respond only to 
the waves radiated from a given transmitter without inter¬ 
ference from waves of other frequencies. This is done by 
making the oscillation constant of the receiving circuits the 
same as that of the sending circuits, and the coupling 
between the two circuits as loose as possible. 

In the arrangement shown in Fig. 102, any stray dis¬ 
turbance in the aerial will act on the detector and cause a 
click in the telephone. 

Advantages of using a Secondary Circuit .—Besides being 
able to place the coherer at the antinode of potential, it is 
possible by using a secondary circuit to damp out a large 
number of the waves of other frequencies that are surging 
in the primary circuit. The oscillation constant of the 
secondary circuit must be the same as that of the primary. 
In the case of the transformer, the interference can be 
diminished by reducing the number of turns of the primary 
and increasing the distance between the primary and 
secondary windings, both being at the expense of sensibility. 
With the Slaby arrangement the only means of decreasing 
the interference is by reducing the inductance common 
to the two circuits; it is more subject to interference 
than the transformer, though more sensitive ; it is 
employed in the ‘ Telefunken ’ system wherever great 
sensibility is required. It is to be noted that the secondary 
circuit has frequently a large amount of inductance, so that 
a single vibration in the primary has very little effect on it. 
Just as a cathedral bell requires a large number of small 


152 


RADIO-TELEGRAPHY. 


impulses before the first sound is made, so a large number 
of vibrations are required in the primary of a receiving 
circuit to set up vibrations of sufficient amplitude in the 
secondary to act on the detector; and the vibrations in the 
secondary that are not completely in tune to the natural 
period get wiped out. 

Shunted Capacity to the Coherer .—In its non-conducting 
state the coherer acts as a very minute condenser, which it 
is impossible to keep constant, so it is necessary to 
shunt it with a capacity, sufficiently large so that the 
capacity of the two condensers in parallel is practically the 
capacity of the shunt. Without this it is impossible to give 
the circuit a definite oscillation constant. This capacity 
also acts to a certain extent as a short circuit to the coherer, 
therefore if made large it diminishes the sensibility; at the 
same time this condenser makes the detector respond only 
to waves of one definite frequency and therefore it is always 
employed in syntonic working. 

Damping in - the Receiving Circuits .—The function of the 
receiving aerial is completely different from that of the 
sending aerial, though usually the same is used for both 
sending and receiving. The function of the sending aerial 
is to radiate energy; the function of the receiving aerial is 
to absorb energy. There is no damping in the receiving 
circuit due to a spark-gap, but there must often be con¬ 
siderable loss due to radiation from the aerial. Both 
the experiments of Duddell and Taylor in England and 
those of Tissot in France go to prove that the damping 


THE RECEIVER—METHODS OF ARRANGEMENT. 153 


due to radiation from the receiving aerial is considerable. 
It is probable that the carpet aerial of Lodge, by radiating 
less, would have a considerably smaller damping decrement 
than the aerial used with coupled systems. De Forest 
since 1908 has been using an arrangement which was a 
good radiator for sending and a 
good absorber for receiving. It 
will be seen from Fig. 108, which 
illustrates the arrangement at 
Skegness, that the aerial consists 
of two sets of wires. These two 
sets of wires are discharged 
through two spark-gaps G for 
sending, but for receiving the 
wires are in series, so that the 
radiating wires are in open cir¬ 
cuit for sending and closed circuit 
for receiving. The tuning box 
to the extreme right of the 
receiving apparatus (Fig. 100) 
consists of two inductances L 

and condenser Ki, the adjust¬ 
ments being made by sliding [Reproduced from Electrical Engineer. 

contacts movable from outside, the Proprietors.] 

so that waves of from 200 to 6,000 feet can be received. 

The electrolytic cell E 1 is used as detector, and it is also 

1 The electrolytic cell is described on p. 174, and the potentiometer 
on p. 180. 



Fig. 108. 























154 


RADIO-TELEGRAPHY. 


in the local circuit which contains the battery ^, potentio¬ 
meter F, and telephone receiver B. 

Subsidiary Circuits .—The simplest method of making 
the oscillations apparent is to shunt the detector with a 
telephone receiver and a Leclanche cell, the alteration of 
the electric properties of the detector causing a change 
of current through the telephone. The potential difference 
of a single Leclanche cell is often too large, as it would 

completely break down 
the resistance of a 
sensitive coherer, mak¬ 
ing the filings conduct¬ 
ing. To obviate this a 
potentiometer arrange¬ 
ment is often used. The 
cell discharges through 
a high resistance A B, 
Fig. 109, and from two 
suitable points A C on this resistance leads are taken through 
the telephone to the coherer. Also, if a receiving trans¬ 
former be used, a condenser F is placed in the middle of 
the secondary to prevent current from the Leclanche cell 
flowing through the transformer. The capacity of this 
condenser should be sufficiently large not to appreciably 
diminish the capacity of the oscillating circuit. Connecting 
the local circuit to the node of potential, there is no tendency 
for the oscillatory current to flow through the local circuit. 
Sometimes the local circuit connexions are made at D, in 

































THE RECEIVER—METHODS OF ARRANGEMENT, loo 


which case two small inductance coils have to be placed in 
the circuit to choke back the oscillatory current. It is 
instructive to note the two different devices, choking coil 
and condenser. The choking coil acts as if it had prac¬ 
tically no resistance to the direct current and infinite resist¬ 
ance to the oscillatory current. On the other hand, the 
condenser acts as if it had no resistance to the oscillatory 
currents, and infinite 
resistance to the 
steady direct current 
from the Leclanche 
cell. 

Relay and Tapping 
Circuits with Coherer. 

—As there are a 
large number of 
stations still fitted 
with coherers on the 
Branly principle, the necessary circuits are depicted in 
Fig. 110. The relay circuit is shown in thin lines, and 
the branch to the tapping circuit in dotted lines. The 
action of the relay A is to close the local circuits when the 
coherer becomes conducting through a recording apparatus, 
generally a Morse inker M, and an electric bell B. The 
bell-hammer IT taps the coherer, making it non-conducting 
again. Whilst vibrations are taking place the coherer is 
being made alternately conducting and non-conducting. 
Just after they cease the bell acts, making the coherer 







































RADIO-TELEGRAPHY. 


lo() 



non-conducting till fresh vibrations take place. The arrange¬ 
ment of circuits is instructive in illustrating one of the 
general precautions necessary in a wireless telegraph station. 











THE RECEIVER—METHODS OF ARRANGEMENT. 157 


/ 


The relay and bell circuits are being continually broken at 
C and D, and as both these circuits contain electro-magnets 
with considerable inductance sparking would occur at these 
points. Now these sparks, however minute, would be 
sufficient to cause a difference of potential across the 
coherer to make it conductive, so it is essential to prevent 
them. This is done by placing non-inductive high resist¬ 
ance shunts R across the gaps, and a condenser K across 
the battery of cells. The condenser F completes the 
oscillatory circuit, and as it 
is in series with the coherer- 
condenser, it is made fairly 
large, so as not to alter the 
oscillation-constant. A set of 
receiving apparatus, as used 
in the Telefunken system, is 
depicted in Fig. 111. Morse 
instruments are sometimes fitted with an arrangement by 
means of which the first signal received sets the clockwork 
in motion, and the tape moving, to be stopped automatically 
at the end of the message. 

Syphon Recorder and Clockwork with Coherer .—In place 
of the relay and Morse inker, which is used in ordinary 
land telegraphy, the Lodge-Muirhead Syndicate use a 
syphon recorder very similar to a pattern used for sub¬ 
marine cable working. Fig. 112 illustrates the circuits. 
The source of potential difference and syphon recorder S 
are in series with the coherer and the secondary of the 


















158 


RADIO-TELEGRAPHY. 


transformer. The oscillatory circuit is completed through 
the condenser T, which also short-circuits the recorder for 
high-frequency currents. 

The Overflow Arrangement of Lodge .—The best syntony 
can be obtained by making the condenser K (Fig. 103) 
large, and using only a few turns on the secondary of the 
transformer D. The oscillations take place through this 
condenser, increasing in amplitude till the coherer is broken 
down. This is in fact the same as the arrangement made 
in Lodge’s experiment, first made in 1890 with syntonic 

Leyden jars. Lodge 
found that by setting¬ 
up vibrations in the 
circuit A, Fig. 113, 
vibrations occurred in 
a Leyden jar circuit 
B nearby. When the circuit B was brought into perfect 
tune with A by moving the slider S along the two parallel 
wires, the amplitude of potential increased sufficiently to 
produce a spark. Lodge called this an overflow. 

Receiving Circuits compared .—The receiving arrangements 
generally used are :— 

(1) Auto-transformer. 

(‘2) Closely coupled magnetic transformer. 

(3) Loosely coupled magnetic transformer. 

The auto-transformer is generally employed with a very 
close coupling, and sometimes nearly the whole of the 
inductance is common to the two receiving circuits. A 


















THE RECEIVER-METHODS OF ARRANGEMENT. 159 


detector in the secondary circuit is responsive to any wave 
of large amplitude, but the damping is excessive. This 
arrangement is used to get into touch with distant stations. 

The loosely coupled magnetic transformer has small 
inductance and a large capacity in parallel with the detector. 


SENDING 


B 

-a 

C 

c 


RECEIVING 


K 


The detector is thus short-circuited, except for slightly 
damped w T aves, which are in such perfect syntony with 
the vibrations set up in 
the secondary circuit that 
the amplitude of the 
vibrations increases suffi¬ 
ciently to act on the 
shunted detector. This 
arrangement is used 
when there is liability to 
interference from atmo¬ 
spheric disturbances or 


C 

j 


V 


□A 


F 

□ 


H 


Fig. 114. 


signalling from other stations. A capacity of half a micro¬ 
farad has been used under special circumstances. 

The closely coupled magnetic transformer is intermediate 
in its action. 

Changing from Receiving to Sending .—The same aerial 
is used both in sending and receiving; but it is most 
important to keep the receiving apparatus completely insu¬ 
lated from the sending apparatus. This is generally done 
by a single switch. It is usual to arrange this so that in the 
sending position the primary receiving circuit is broken in 
two places : the potentiometer circuit is broken and the 



















160 


RADIO-TELEGRAPHY. 


detector short circuited. Fig. 114 shows diagrammatically 
how this can be done in one operation by a three-pole throw- 
over switch. The outer levers would consist of metal bars 
connecting A to B and F to C, completing the secondary 
sending; these bars in the receiver position would connect 
A to K and F to L, completing the primary receiving circuit. 
The third arm of the switch is made of insulating material, 
with two small copper strips. In the sending position one 
of these completes the primary of the transformer, or induc¬ 
tion coil through D E, and the other short-circuits the 
coherer through J I. On the receiver one of these strips 
completes the local battery circuit through G H. 

The Poulsen-Pedersen Arrangement .—Detectors always 
form a point of relatively high resistance in the receiving 
circuit. This is an advantage in ordinary systems, as the 
detector thus absorbs the energy of the damped oscillations. 
In the case of the Poulsen arc the energy emitted is 
practically continuous, so the receiving circuit also vibrates 
continuously. The less the damping the greater the 
accumulation of energy in the circuit. In the chapter on 
sending it has been pointed out that close coupling increases 
the damping of the oscillations. With continuous waves 
it is both feasible and advantageous to use a very loose 
coupling between the primary and secondary receiving 
circuits to reduce the damping. 

To still further reduce the damping the detector is placed 
in a tertiary circuit, which is momentarily closed after 
energy has accumulated in the secondary circuit. This 


THE RECEIVER—METHODS OF ARRANGEMENT. 161 


is done by means of what is called a ticker, which generally 
consists of a revolving toothed wheel whose teeth make 
intermittent contact with two thin gold wires. 

For a potential detector the ticker can be placed as shown 
in Fig. 115. The vibrations in the circuit ABC gradually 
increase in amplitude till at an arranged time the ticker 
circuit is momentarily broken at B, causing a breakdown of 
the coherer resistance. The condenser K prevents the flow 



of current from the cell D flowing through the ticker, and 
the choking coils F F offer a path of practically infinite 
resistance to the oscillatory currents. Thus normally 
rapidly augmenting currents are surging in ABC, being 
momentarily shifted through the coherer, allowing current 
from the battery also to flow through the coherer and 
recorder B. 

With a current detector the ticker is placed in the tertiary 
circuit, so that the vibrating circuit is never broken. One 


E.T. 


M 



























162 


RADIO-TELEGRAPHY. 


method is shown in Fig. 116. The capacity of the con¬ 
denser Iv is relatively large and of the order of one-fifth of a 
microfarad, so that when the ticker B makes contact the 
condenser C is practically short circuited, all the energy 
being shunted across the telephone T. 





10 T 


Fig. 117. 

The method, however, recommended by Poulsen, on the 
score of simplicity and certainty, is to use a telephone as 
the detector, connecting it as shown in Fig. 117. In this 
arrangement it will be seen the telephone T is momentarily 
shunted across the capacity C. 


















CHAPTER IX. 


THE RECEIVER-THE DETECTING APPARATUS AND OTHER 

DETAILS. 

History .—At first only instruments for detecting small 
differences of potential were used. Hertz employed a 
minute spark gap, a most insensitive arrangement, but 
which served his purpose admirably for the few yards 
over which he worked, and it also formed a rough mode of 
measuring the energy received. A much more sensitive 
detector had been discovered by Munk in 1835. He 
found that the discharge of a Leyden jar decreased the 
resistance of filings of certain substances, but that the 
original resistance was restored when the filings were 
shaken. Branly rediscovered this action in 1890, and 
Lodge about the same time found that two knobs placed 
sufficiently close together were made to cohere by the 
action of the discharge, hence he named this form of 
detector a coherer. The tapping back, always an objection 
in this type of instrument, was overcome by Lodge by 
rotating one of the materials, and by Castelli in 1901 by 
using an iron cylinder containing two blocks of carbon 
separated by a globule of mercury. This arrangement was 
found to decohere when the wave ceased ; but, on the other 


164 


RADIO-TELEGRAPH Y. 


hand, it soon lost its sensitiveness. The forms of detectors 
now most commonly used are the electrolytic detector 
invented by Neugschwender and Aschkinass in 1898, with 
the modified forms of Schlomilch and De Forest : the 
barretter of Fessenden, the magnetic detector of Rutherford, 
made practical by Marconi, and the well known micro- 
phonic detector of Hughes. 

The Function of the Detector .—It has been seen from the 
last chapter that the function of the receiving circuit, taken 
as a whole, is to re-transform electro-magnetic waves 
travelling through the aether into electric vibrations along 
a wire. A detector is for the purpose of making these 
vibrations apparent, and if placed in an oscillatory receiving 
circuit it dissipates most of the energy of the vibrations; 
at the same time the more quickly it dissipates the energy 
the greater the damping and consequent liability to be acted 
on by waves of various frequencies. A compromise has to 
be effected between the two opposing qualities, and thus it 
will be seen how impossible it is adequately to compare the 
detectors used by various companies. The best form of 
detector depends greatly on the wave length and damping 
of the sending circuit; generally the greater the damping 
in the sending circuit the larger should be the resistance of 
the receiving detector. For example it was found in two 
different sets of experiments, using very similar sending 
circuits, that the best resistance for the detector was about 
60 ohms. Large alterations of some property of the 
detector with minute electric vibrations and at the same 


THE DETECTING APPARATUS. 


165 


time reliability are requisite. Electrically, detectors may be 
grouped into two classes. In the first and earliest used, the 
potential difference at the terminals has to rise to a certain 
critical value ; in the second form the current alters some 
property of the detector. 

Difference of Potential Detectors .—This class of detector 
is placed at the antinode of potential of a receiving oscillating 
circuit, and it is also in a subsidiary circuit containing 
a battery with either telephone, Morse inker or syphon 
recorder. Under normal conditions it is practically an 
infinite resistance in the battery circuit and a small con¬ 
denser in the oscillating circuit. To make this class of 
detector work, all that is required is a critical difference of 
potential. Below this critical value the resistance to direct 
currents is infinite ; above it this resistance is practically 
nothing. With most forms of this detector the resistance 
has to be made infinite again by some mechanical means. 
The detector, when on the receive, is permanently in circuit 
with a battery not quite powerful enough to break down its 
resistance. The action of the oscillatory current is to 
increase this voltage at the terminals sufficiently to make 
the detector conducting, thus allowing a flow of current 
from the battery to work either recorder or telephone. On 
account of the joining together of the particles of matter 
after the electric discharge these detectors are called 
coherers. 

Theory of the Coherer .—A great deal has been written on 
the theory of the coherer. In J. J. Thomson’s theory of 


1GG 


RADIO-TELEGRAPHY. 


matter each molecule consists of a large number of electrified 
corpuscles; even in a molecule of metal these are in rapid 
motion, hut they do not leave their molecule on account of 
electrostatic attractions. Guthe considers that an external 
electrostatic field will assist corpuscles to leave their mole¬ 
cules due to increase of kinetic energy ; a vibratory electric 
current helps the passage of corpuscles from molecule to 
molecule of the metal. This current pushes aside the 
dielectric, thus causing a continuous metallic conductor to 



he formed. The tapping of the coherer brings into contact 
fresh molecules of metal, between which the dielectric has 
not been pushed aside. Where the surface over which 
coherence takes place is very small, the detector is to a great 
extent self restoring, and requires no tapping back, though 
it gradually becomes more and more insensitive. In this 
case Guthe supposes that most of the passage of electricity 
is through the gas surrounding the molecules, which is made 
conducting by the electric vibrations. In many coherers 
both actions are observable. 

Branly's Coherer .—This has now only historical interest, 
but for a long time it and its modifications were the only 




































TIIE DETECTING APPARATUS. 


167 


practical detectors available. It essentially consists of a 
tube of filings making a series of bad contacts, the tube 
having a path of high or infinite resistance, with a low 
potential at its terminals, but the resistance breaking down 
completely with a higher difference of potential. With the 
source of increased potential removed, the resistance still 
remains low, and the tube has 
to be shaken for it to regain its 
original high resistance. The 
critical pressure depends on the 
material used. Trowbridge, in 
1899, showed that with twenty 
steel contacts in series eight volts 
were required, and later Gutlie 
found the critical voltage per con¬ 
tact for various substances lay 
between 0’05 and 0‘25 of a volt. 

The typical coherer consists of two metal plugs in a 
vacuum tube separated one or two millimetres, the space 
between being partly filled with filings. Marconi uses 
amalgamated silver plugs separated by a mixture of nickel 
and silver filings; his coherer is shown in Fig. 118; his 
coherer holder and tapper in Fig. 119. Dr. W. H. 
Eccles, a leading authority on the coherer, points out the 
long training and great skill required to make a good 
coherer ; even the changing of an old file for a new one 
in the making of the filings alters the behaviour of the 
coherer turned out. Dr. Eccles also found that to get the 












168 


RADIO-TELEGRAPHY. 


best results the filings arrange themselves in conducting 
chains more easily if moving slightly, as may he caused hy 
a vibrating tube, and that the smaller the area of the 
filings with consequent high initial resistance, the more 
sensitive becomes the coherer. He gives the initial 
resistance of a modern coherer as 100,000 ohms. 

There are several disadvantages to this type of coherer. 

(1) It requires a relay with tapping back arrangement. 

(2) Coherers vary greatly in reliability and sensibility. 

(8) Whilst transmitting, the filings are very liable to 

become permanently cohered from powerful vibrating 
currents set up in the connecting wires; hence in practice 
they have to be fixed in a specially-made metallic box, and 
the wires to the coherer have to be covered with lead, which 
is connected to the metal of the box. 

(4) The coherers work best, sometimes horizontally and 
sometimes vertically, the same coherer frequently requiring 
shifting. 

The Lodge-Muirhead Coherer .—This is a great advance 
over the filings coherer, and is being used in a number of 
stations. 

This coherer is shown in Fig. 120. It consists of a 
slowly revolving steel disc a, rotating extremely close to a 
globule of mercury h, but separated from it by so thin a film 
of oil that the insulation is broken down by about three 
quarters of a volt; it is connected across a potentiometer 
and battery, so as to have a third of a volt across its termi¬ 
nals. An increased difference of potential due to the electric 


THE DETECTING APPARATUS. 


169 


JHH. 



-DTI 


l^vVWvvJ 


g 

A -r 

...J. 


Plan 


. 




vibrations in the receiving circuit causes a complete break¬ 
down of resistance, but immediately the vibrations cease 
this again becomes infinite as the wheel revolves. It is 
important to make perfect elec¬ 
trical contact between the mercury 
and outside circuit; this is done 
by the platinum spiral c, con¬ 
nected into the terminal h, which is 
screwed into the mercury trough d. 

The other connexion is made by 
the copper brush e, resting on 
the coherer axle,/. To keep the 
edge of the coherer disc perfectly 
clean a cushion of felt k, carried 
from a spring /, rests lightly on 
it. The steel disc is geared by 
the ebonite wheel fj to clockwork, 
which also drives the syphon 
recorder tape, and in the latest 
pattern a special interrupter is 
used in circuit with a telephone 
receiver; these instruments have 
the recorder and a telephone in 
parallel. In this case the steel disc is notched evenly along 
the circumference, and an interrupter making about 400 
revolutions per minute breaks the telephone circuit for 
about 40 J 00 a second during each revolution. 

Though not so simple as Marconi’s magnetic detector, the 



Eig. 120. 













































170 


RADIO-TELEGRAPHY. 


author lias found this coherer very reliable over a period of 
two years’ observation. 

To use the coherer the following instructions are recom¬ 
mended by the makers :— 

To adjust the coherer for use, remove the caj) which 
covers the mercury globule, screw up the reservoir until 
the mercury is just touching the edge of the steel disc, and 
drop as little as possible of the “ special ” heavy oil, by 
means of a large needle, on to the disc after setting it in 
rotation, thus allowing the oil to film nicely over the surface 
of the mercury. 1 The mercury should on no account be 
touched with a copper or brass wire. 

In adjusting the coherer— 

(1) The steel disc should be immersed in the mercury as 
little as possible, otherwise the coherer will be too insensi¬ 
tive, and the signals will tend to run into one another. 

(2) It is important to see that the steel disc of the coherer 
is connected to the positive pole of the battery. 

(3) It is important to see that the connexion between the 
mercury and the amalgamated platinum spiral in the 
ebonite reservoir is a thoroughly good one, otherwise the 
signals will be imperfect and irregular. If, after oil has 
been poured on the mercury, the reservoir should be turned 
over or emptied of its contents accidentally, some oil is 
almost certain to run down and “film over ” the platinum 
spiral, so that on refilling the reservoir with mercury the 

1 Too mucli oil on the mercury tends to make the coherer insensitive ; 
when there is too little the signals run into one another. 


THE DETECTING APPARATUS. 


171 


contact between the latter and the platinum spiral becomes 
bad and the signals received unsatisfactory. To re-amal¬ 
gam ate the platinum spiral, all that is necessary is to heat 
it in a Bunsen or methylated spirit flame to a bright red 
heat and then plunge it into pure mercury. The amalga¬ 
mation is satisfactory when the mercury adheres to the 
platinum, and can only be shaken out of the spiral with 
difficulty. Before replacing the platinum spiral in the 
ebonite reservoir the latter should be carefully cleaned with 
paraffin oil and dried. 

(4) It is important that the edge of the steel disc of the 
coherer should be keen and free from notches or indents. 

(5) The speed of the coherer wheels affects the signalling. 
If it be rotating too fast the short signals may only result 
in a slight flick of the syphon needle, but for rapid signalling 
the coherer must also rotate fairly quickly. Three pairs of 
ebonite change-wheels for the coherer and three corre¬ 
sponding pairs of brass ones for the clockwork are sent out 
with each set. 

Auto-coherers .—This is the name given to coherers that 
require no tapping back. They are very uncertain, but the 
one invented by Signor Castelli, of the Italian Navy, is of 
historical interest, on account of it being used by Marconi 
in his original experiments on signalling across the Atlantic. 
It consisted of electrodes of iron or carbon separated by a 
globule of mercury, with a telephone in the local circuit. 
The pressure of the electrodes on the mercury could be 
adjusted by means of a screw. 


172 


RADIO-TELEGRAPHY. 


The Auction of De Forest }—De Forest has lately used two 
platinum discs, with sides parallel, placed about 2 milli¬ 
metres from either side of the filament of an incandescent 
lamp. He claims that this type of detector can be made 
extremely selective to signals not only of waves of different 
frequencies, but also to different spark frequencies depending 
on the battery pressure and distances of plates from the 

filament. De Forest states that he 
found the audion has to be placed at 
the antinode of potential, and the 
action depended on the total energy 
received. The method of arrangement 
is shown in Fig. 121; G is a galvano¬ 
meter and T a telephone receiver. 

Current Detectors .—The more com¬ 
mon forms of detector now used owe 
their action to changes of current in 
the vibratory circuit. Sometimes the 
action is such that the actual energy of the oscillations is 
used as in measuring instruments, and in the magnetic 
detector; but more often the action is to increase or decrease 
the current through a local circuit containing a battery and 
telephone receiver. Current detectors with a high resist¬ 
ance are placed at the antinode of potential. 

The Magnetic Detector. —Rutherford, in 1897, found that 
the properties of a strongly magnetised needle were altered if 
placed in a solenoid through which electric vibrations took 
1 Fleming claims priority in this invention. 



[Reproduced from Electrical 
Engineering of Feb. 14,1907, 
by permission of the Pro¬ 
prietors.] 





















TIIE DETECTING APPARATUS. 


173 


place, but with each succeeding vibration the alteration 
became rapidly less. Marconi made the instrument prac¬ 
tical as a radio-telegraph receiver by using a slowly moving 
iron band, magnetised by induction, passing through the 
solenoid, through which the oscillations take place. Marconi’s 
instrument consists of a solenoid (Fig. 122) in the radio¬ 
receiving circuit. This solenoid is about inch diameter and 
several inches long; it consists of a single layer of wire 
wound on a glass tube, 
the best proportions and 
amount of wire on the 
bobbin depending on the 
wave - length. Through 
this solenoid passes an 
endless core of fine iron 
wires, revolved by clock¬ 
work as slowly as possible over pulleys. These iron wires 
are magnetised by two small horse-shoe magnets. Round 
the solenoid is a bobbin wound with fine wire of several 
hundred ohms resistance, and connected to a telephone 
receiver. The oscillatory current alters the number of 
lines of magnetic force in the iron and through the bobbin, 
causing a current and a click in the telephone. 

According to Dr. Eccles the sudden change of the 
magnetic field caused by the oscillatory current is in the 
same direction as the slower change produced by the moving- 
band in the permanent magnetic field; and therefore the 
iron should not be too strongly magnetised when acted on, 



Ei"- 


122 . 


[Reproduced from Electrical Engineering of 
Feb. 7, 1907, by permission of the Pro¬ 
prietors.] 






















174 


RADIO-TELEGRAPHY. 


but with a given force applied the rate of change of induction 
should be as large as possible. Dr. Eccles also finds that the 
effect is proportional to the whole energy of the train of oscil¬ 
lations, but he could at the same time obtain more powerful 
sounds with largely damped waves of greater initial ampli¬ 
tude. It is, however, claimed by Marconi that in practice 
this instrument can be made effective to only long trains of 
undamped waves, and if as is generally shown it is placed 
directly in the aerial circuit this must be so, or atmospheric 
disturbances would cause greater interference than is the case. 

It will be seen that with Marconi’s magnetic detector there 
is nothing to get out of order and no adjustments are required. 

The Electrolytic Detector . 1 —In 1898 Neugschwender and 
Aschkinass found that when the plating on a piece 
of mirror was cut by a sharp razor and subjected to a 
small difference of potential, no current passed so long as 
the surface of the glass was dry, but with the glass 
moistened it could be seen with the aid of a microscope 
that minute metallic particles were torn off from the anode, 
forming bridges across the gap, and decreasing the resistance 
of the circuit. If this arrangement be placed in a receiving 
oscillatory circuit these currents will decompose the water, 
and the evolved gas will break down the bridges, thereby 
increasing the resistance so long as the oscillations last. 

1 The process of decomposing a liquid by means of an electric 
current is called electrolysis ; the ends of the wires dipping into the 
liquid or electrolyte are called electrodes. The positive electrode 
where the current enters the liquid is the anode; the negative electrode 
where the current leaves the electrolyte is the cathode. 


THE DETECTING APPARATUS. 


175 


De Forest found that a more sensitive arrangement was, 
after the formation of the bridge, mechanically to separate 
the electrodes. There was then a back E.M.F. acting in 
an opposite direction to the battery cell supplying the 
current. If this be now placed in the receiving circuit 
the oscillatory current causes a temporary annulment of 
the back E.M.F., allowing current to pass through a 
telephone receiver in the battery circuit. 

Instead of surfaces Schlomilch in Germany and Fessenden 
and De Forest in America have used a single fine platinum 
wire as the anode, and sulphuric acid as the electrolyte. 
This form has been very largely used by the Fessenden, 
De Forest, and German companies. 

The Lead Peroxide Detector of Brown .—This detector is 

of the electrolytic type. It consists of a pellet of lead 

peroxide (Pb 0 2 ) placed between small blocks of lead and 

platinum, the lead being at the end of a spring, so that its 

pressure on the peroxide may be regulated by a screw to 

obtain the best result. The positive pole of the local 

battery has to be connected to the platinum, and the 

inventor finds two volts to be the best pressure for this 

batterv. 

«/ 

According to Brown two actions occur. The local battery 
tends to break up the peroxide into lead and oxygen, the 
lead being deposited on the lead cathode and oxygen on 
the platinum anode. The peroxide cell, on the other hand, 
acts as a battery, tending to cause the lead to be deposited 
on the anode and oxygen on the cathode. Under normal 


176 


RADIO-TELEGRAPHY. 


conditions the action of the local battery is the more 
powerful, but an oscillatory current enhances the action of 
the peroxide cell, so lead is actually deposited on the 
platinum, to be removed by the action of the local battery 
so soon as the vibrations cease. During the oscillations 
the electrical effect is an apparent increase of resistance of 
the peroxide cell. 1 

Fessenden s Barretter .—Professor Fessenden 
has used a very fine platinum filament A. 
(Fig. 12B) for detecting oscillatory currents. 
The size used was about O’OOOl inch in dia¬ 
meter, and rather less than an inch long, 
having a resistance of about 60 ohms. The 
barretter is also connected through a local 
circuit containing a battery and telephone re¬ 
ceiver. The current due to received waves 
increases the temperature and resistance of 
the filament, decreasing the current through 
the telephone. The objection to this type of instrument 
is its liability to being burnt out; to obviate this Fessenden 
used a filament of weak acid (Fig. 124) which, besides being- 
more reliable gave a greater change of resistance with a 
given oscillatory current. This type of detector has a 
very high resistance, as much as 80,000 ohms even whilst 



METAL 


Fig. 123. 

[Reproduced 
from Electrical 
Engineering of 
Feb. 7,1907, by 
permission of 
the Proprie¬ 
tors.] 


1 The author using this detector found the opposite effect, a decrease 
of resistance; he also found that the detector would not work efficiently 
with a greater battery pressure than half a volt. The normal resist¬ 
ance of this detector is about 10,000 ohms. 











THE DETECTING APPARATUS. 


177 



the vibrations are taking place, and the current flowing 
through the local circuit is about one-tenth of a milliampere. 

The Microplionic Detector. —In 1878 Hughes found that 
a loose contact, if properly set and placed in a battery 
circuit, was subject to change of resistance with changes of 
pressure. As used in radio-telegraphy the microplionic 
detector consists of a hard carbon point 
pressing lightly on a steel spring. The 
detecting action may be due to heating at 
the point of juncture between the carbon 
and steel, but it may also be partly thermo¬ 
electric and partly due to the carbon acting 
as a rectifier. The resistance of this detector 
is of the order of from 10 to 100 ohms. 

Thermo-electric Detectors .—L. W. Austin 
has found that the contact between two 
elements differing widely in the thermo¬ 
electric series makes an effic ient radio-telegraphic detector 
He found the best elements to be aluminium against tel¬ 
lurium ; and that greatly increased sensitiveness and con¬ 
stancy of action were obtained by slowly rotating the point of 
contact. The resistance of such a detector is from 1,000 to 
3,000 ohms; the surfaces have to be kept clean with 
petroleum. 

The Carborundum 1 Detector .—H. Braudes, in 1906, found 


Fig. 124. 

[Reproduced from 
Electrical Engi¬ 
neering of Feb. 7, 
1907, by permis¬ 
sion of the Pro¬ 
prietors.] 


1 Carborundum is a carbide of silicon. It is the next hardest sub¬ 
stance known to the diamond, and is made in electric furnaces at 
Niagara. 


R.T. 


N 












178 


RADIO-TELEGRAPHY. 


that, in general, conductors in which the current does not 
vary proportionally to the applied E.M.F. are capable 
of acting as detectors owing to their rectifying effect, which 
makes the conductor have less resistance in one direction 
than the other ; in fact, it is often thought that the con¬ 
ductivity of such a substance is electrolytic. Pierce, in 
1907, found that with 10 volts at the ends of a crystal of 
carborundum the current in one direction was 100 micro¬ 
amperes, but with the E.M.F. reversed the current was 
only 1 micro-ampere. Platinising the two ends of the 
carborundum a much lower total resistance was obtained, 
and the excess of current in one direction over the other 
was greater, though there was a smaller efficiency of recti¬ 
fication. General Dunwoody, of the United States Army, 
has used this detector without any local battery, simply 
shunting the carborundum with a telephone. 

The Telephone Receiver .—A telephone receiver consists 
essentially of an extremely thin disc of iron in the field 
of an electro-magnet. Rapid variations of current through 
the electro-magnet cause varying attractions of the iron 
disc, and these movements of the disc are imparted to the 
air as sound waves. One characteristic of the telephone 
receiver is that it is much more sensitive to minute changes 
of current than to minute initial currents. With spark tele¬ 
graphy it has been impossible to use the telephone receiver 
directly as a detector; it always has to be placed in a local 
circuit, through which, in the majority of detectors, a 
current constantly flows ; and the electric properties of 


THE DETECTING APPARATUS. 


179 


some substance in the circuit has to be altered, changing 
the current through the telephone. 

With the undamped waves of Poulsen, however, it is 
possible to accumulate sufficient energy in the vibratory 
circuit, so that if the current be momentarily broken 
through a telephone receiver, the energy of the oscillatory 
current is sufficient to cause the necessary sounds. 

Potential versus Current Detectors .—At the present stage 
of our knowledge it is almost impossible to adequately com¬ 
pare different detectors. It has been seen how with a 
special system the ordinary telephone receiver may be used; 
the choice of other detectors should depend on the character 
of the sending circuit. The resistance of the potential 
indicator is generally high, and as usually connected up, it 
requires waves of comparatively large amplitude ; accord¬ 
ingly it is admirably adapted for use with the original 
Marconi aerial, where sharp tuning is not required and the 
circuit is not subjected to extraneous disturbances. The 
action of the current detector on the other hand usually 
depends on the total energy absorbed by the detector; it 
therefore can be used for long trains of waves of small 
amplitude in cases where good tuning is essential. 

One advantage of the potential detector is that it can be 
easily used with recording and calling-up apparatus on 
account of the great change of ohmic resistance. With 
current detectors this change is always so small that hitherto 
a telephone receiver is the only indicator that has proved 
satisfactory. Where rapid signalling is necessary the tape 

n 2 


RADIO-TELEGRAPHY. 


iso 


however has to be discarded, as the maximum speed of 
receiving at present is about fifteen to twenty words 1 a 
minute, whilst a good operator can read thirty-five words a 
minute with the telephone, eliminating noises from atmo¬ 
spheric disturbances by the different character of the sound. 

Testing the Detector .—It is most important to see that 
the detector is in good working condition from time to time. 
This can be easily done by having a miniature oscillator a 
foot or so removed from the detector. This oscillator con¬ 
sists of an ordinary electric bell or buzzer worked by one or 

two dry cells with a key in circuit, and 
an aerial about one foot high connected 
to one of the terminals across which the 
spark occurs. 

Beg illat ion of Local Circuit. — Some 
detectors work with a considerable range 
of adjustment of the battery power in 
the local circuit; others require a rather fine adjustment, 
more especially when the pressure required is only a fraction 
of a volt. In this case a potentiometer is used as shown 
in Fig. 125. The current from one or more cells is taken 
through a high resistance, which can be tapped at any con¬ 
venient point. In the instance given the potential of the 
cell is 2 volts ; the tapping is taken one-tenth of the distance 
along the resistance, so that the pressure at the terminal of 
the detector is one-fifth of a volt. 

Calling-up Arrangement .—It is often convenient to have 
1 A word is always taken as having- five letters. 


rKh 
a 

fVWWWVWW 

-1 


Fi" 125. 







THE DETECTING APPARATUS. 


181 


a calling-up arrangement on the receiver. This is more 
easily arranged with the coherer than with current detectors. 
Fig. 126 illustrates the Lodge-Muirhead arrangement with 
coherer and recorder. In addition to the galvanometer 
bobbin A for recording, there is a half-turn of wire E which 




is connected to the metal disc C ; a rod 1) can be rotated so 
that the arm B at the end comes close to C. When a signal 
makes the coherer conducting the circuit is completed 
through the bell and battery. The hell starts ringing and 
continues owing to the spark of the hell keeping the coherer 
conducting till the rod is rotated, moving the arm away 

















































































182 


RADIO-TELEGRAPHY. 


from C. The switch is then moved so as to take the rod D 
out of action. The method of suspending the coil is shown 
in Fig. 127. At the bottom, fixed to a small aluminium 
plate, is the syphon. 

Sullivans Relay— Mr. H. W. Sullivan has lately placed 
on the market a relay which may he used either for calling- 
up, or for signalling up to thirty words a minute hand send¬ 
ing. For signalling the relay is guaranteed to work with one 



Fig. 128. 


Leclanche cell through 250,000 ohms, and as a call relay it 
is guaranteed to ring a bell in a local circuit with one 
Leclanche cell through five megohms. The relay consists of 
a moving coil galvanometer with pivoted bearings, of which 
the general appearance is shown in Fig. 128. To the moving- 
coil is fastened a very light aluminium arm with platinum 
contact piece. A current through the moving coil causes 
the arm to swing against a fixed platinum contact. The 
great sensibility that can be obtained is due to springs 
fastened to both the moving and fixed arms, which cause 




























































































THE DETECTING APPARATUS. 


183 


them to yield slightly when contact is made, thus pre¬ 
venting any rebound ; these springs also make the contacts 
self-cleaning. Further details may be gathered from Mr. 
Sullivan’s instructions, which are as follows :— 

(1) To remove cover of instrument, turn anti-clockwise 
about J-inch, then lift. 

(2) The coil is pivoted in sapphire bearings, and is 
roughly balanced by means of the counterpoise on the back 
end of the contact-tongue, an exact balance being after¬ 
wards effected for ship-board use by means of the adjustable 
leaden arms soldered to the coil frame, front and back. 

(8) To vary sensibility— 

Move inward or outward the longer end of the brass 
adjusting lever. 

The shorter end of this lever is pinned to the outer end 
of a non-magnetic hair-spring, surrounding and attached at 
its inner end to the upper pivot rod, so that, on moving the 
brass arm in or out, the spring is tightened or loosened, 
the controlling force which the latter exerts upon the coil 
system being correspondingly increased or reduced. 

(4) The white wire spirals from the two front terminals 
complete the line circuit through the non-magnetic hair¬ 
spring and the fine silver ribbon at bottom of coil; while 
the two green wire spirals connected to the back terminals 
marked “Local” complete the local circuit through the 
S-shaped attached spring of contact lever and the platinum 
contact screw in brass cock piece. 

(5) Both line and local circuits are protected by means of 


184 


RADIO-TELEGRAPHY. 


fuses in glass tubes. In the event of either fuse being 
blown it can be instantly replaced with a spare one. 

(6) False contact due to mechanical vibration is remedied 
by slightly moving the brass adjusting arm inward. Or, 
the entire instrument may be mounted, without screwing 
down, upon a pad or bed of hair-felt (two or three thick¬ 
nesses). 

(7) The platinum contacts, being burnished, should be 
cleaned when necessary with letter paper (not emery) first 
moistened with spirit, then dried. 

Practical Details .—It is essential to have every joint 
perfect, and the leads should be placed as symmetrically as 
possible. The aerial is common to both sending and 
receiving circuits; the rest of the receiving circuit should 
be entirely disconnected from the sending circuit when 
transmitting, as shown in diagram of main switch (Fig. 114). 
The receiving leads should be kept far removed from the 
sending leads. Whilst sending, the local circuit through the 
detector should be broken, and often it is advantageous to 
short circuit the detector at the same time. The receiving 
transformer should be wound with very fine stranded wire 
to prevent eddy currents; very little insulation is required, 
so silk-covered wire is used, but only one layer should be 
employed. The best syntonic results are obtained with as 
few turns of wire on the primary as possible; one to three 
turns will often be enough ; also the further the primary 
and secondary windings can be removed from each other 
the better. 


THE DETECTING APPARATUS. 


185 


Instead of a single layer of wire on a bobbin the secondary 
has sometimes been wound in the form of a flat spiral. 

Generally the variable inductance required for receiving 
also consists of a single layer of wires wound on a bobbin, 
with plug connexions arranged so that more or fewer turns 
may he used, with the remainder of the winding short 
circuited. More lately two concentric coils have been used 
whose planes may be relatively changed, so that the self- 
induction of the whole can be altered without altering the 
ohmic resistance of the circuit. 

When close coupling is employed, the capacities used for 
shunting a potential detector are of the order of a few 
centimetres. Those used for tuning in the receiving 
circuits are of the order of one-hundredth of a microfarad, 
and those used to short circuit recording apparatus are 
about one-fifth of a microfarad. 

A station is generally designed for a special wave length 
so as to have the circuit as far as possible symmetrical about 
the spark gap and receiving transformer. To receive waves 
of higher frequencies the oscillation constant of the primary 
is decreased by placing a variable condenser in series with 
the aerial ; to receive longer waves inductance is added. 
The secondary circuit can always be brought into tune by 
altering the inductance or the capacity. 


CHAPTER X. 


MEASUREMENTS IN RADIO-TELEGRAPIIY. 

Subsidiary Apparatus .—It is important that the correct 
current at a proper pressure be given to the induction coil 
or transformer. To enable the operator to see at a glance 
that this is being done, a dead-beat ammeter and voltmeter 
should be placed in the primary supply circuit. It is also 
advisable to have a linesman’s detector, Wheatstone bridge, 
and ohmmeter for testing the continuity, resistance and 
insulation resistance of the circuits. 

Ammeter in Sending Circuit .—To obtain the adjustment 
of greatest energy of vibration in an oscillatory circuit con¬ 
taining an air-gap, the first rough adjustment may be 
obtained by the appearance and sound of the spark, but a 
more sensitive method for any oscillatory circuit is to place 
a hot-wire ammeter at or near the antinode of current. 
The ammeter should have low resistance or it will itself 
cause damping and lowering of the energy. If the wire of 
the ammeter be larger than No. 40 S.W.G. the resistance 
will be greater to oscillatory currents, and for accurate 
measurements the ammeter will require special calibration; 
but for general purposes only the relative current is required. 
When, during the measurements, alterations of capacity or 


MEASUREMENTS IN RADIO-TELEGRAPHY. 


187 


inductance are made, the ammeter must be placed at the 
antinode; for other measurements anywhere near the anti¬ 
node will be suitable. Any adjustment, such as adding self- 
induction, alters the position, and the fresh antinode has to 
be found by trial. Fig. 129 shows an aerial circuit with 
ammeter at antinode of current. Increasing, say, the induc¬ 
tance I, might improve the circuit; but the antinode would be 
shifted, so that if the ammeter were left in the same position 
the apparent energy of oscillations would 
be decreased. The ammeter should be 
shifted along the inductance (Fig. 130) 
until the maximum reading possible is 
obtained. Placing the ammeter at the 
antinode is always the most sensitive 
arrangement, but when it is not neces¬ 
sary to find the inductance or capacity 
that gives the greatest surgings in the 
circuit the ammeter may be placed any- 130> 

where near the antinode ; and so long as neither capacity nor 
inductance are changed the readings are comparable. The 
more a circuit is loaded with capacity, the less is the change 
of current reading caused by shifting the ammeter a short 
distance from the antinode. In the case of the single aerial 
the change is very great, so that it is most important in 
the case of the receiving circuit to insert the receiving- 
transformer or detector at the exact antinode. 

Obtaining the maximum ammeter reading near the 
antinode forms a rough but effective indication of the 










188 


RADIO-TELEGRAPHY. 


surgings in the circuit. As increased energy is supplied, 
say, through an induction coil, the reading of this ammeter 
rises rapidly till a maximum is obtained; the readings again 
rapidly falling off as the energy supplied becomes too much, 
and arcing takes place across the gap. It must, however, 
be remembered that different receiving arrangements require 
different classes of vibrations in the sending circuit, one 
working best with a largely damped violent surge of large 
initial amplitude, whilst another requires a long train of 
waves which may be of much smaller amplitude ; more¬ 
over, the function of an aerial circuit is to radiate energy, 
and if it has too contracted a field of force it may radiate 
very little energy, and yet the ammeter might show large 
vibratory currents ; it follows that it is impossible by this 
means to compare different systems or arrangements of 
circuit. It is best used as a means to tell whether the 
proper amount of energy is being supplied to a given 
circuit, and to obtain the best arrangement with a given 
system. 

Ammeter in Receiving Circuit .—Most important results 
have been obtained by placing an ammeter in the receiving 
aerial. In practice two difficulties arise; the instrument 
must be extremely sensitive, as the currents to be measured 
are very minute; and with the most sensitive instrument it 
is impossible to measure the current over such distances 
as signals can be received. To make the measuring 
instrument as sensitive as possible its resistance must 
have a specified value. Tissot considers from his 


MEASUREMENTS IN RAUIO-TELEGRAPIIY. 


189 


experiments that the resistance of the instrument should 
be such that the total energy dissipated in the circuit is 
equal to the radiation from the circuit, that is, the receiving 
aerial. 

As a special instance, using very similar arrangements, 
Duddell and Taylor in England and Tissot in France found 
the best results, or rather the most energy to work a 
detector were obtained, with a measuring instrument whose 
resistance was about 50 ohms, though different types of 
measuring instruments were used. From this result both 
sets of experimenters considered that a part of the damping 
in a receiving circuit is due to radiation from it. In 
Duddell and Taylor’s experiments with sending arrange¬ 
ments constant and receiving circuit in tune the following 
results were obtained :— 


Resistance of 
Receiving Circuit 
in Ohms, 
r. 

Current in 
Micro-amperes. 

Micro-watts. 

Calculated 

Micro-amperes. 

5*55 

1,958 

21-3 

1,950 

35*9 

1,269 

57-9 

1,306 

66’6 

995 

65-9 

979 

97-0 

795 

61-3 

784 

970 

784 

596 

784 

135-1 

628 

53-3 

628 

196-2 

475 

44-3 

476 


The calculated micro-amperes were found from the 

0 * 1‘2 

empirical formula C = —.— where r is the resistance of 

1 5b -J- r 

the receiving circuit. These experiments show how the 












190 


BADIO-TELEGRAPHY. 


best tuning is obtained by making r as small as possible, 
but the most energy is utilised when the receiving instru¬ 
ment had a resistance of 56 ohms for the particular aerial 
used. From the formula, Messrs. Duddell and Taylor point 
out that the current flows as if an E.M.F. of 0'12 volts 

were induced in the air wire, and that it dissipated energy 

* 

as if it had a resistance of 56 ohms ; they also point out, 
if this constant 56 could be reduced, both the sharpness of 
tuning and the power available for working the detector 
would be increased. 

The following additional data are useful with reference to 
the foregoing experiment : — 

Height of transmitter wire, 42 feet. 

Height of receiver wire, 56 feet. 

Distance between wires, 1,245 feet. 

Current in transmitter wire, 0‘486 ampere. 

Wave-length radiated, 400 feet. 

Number of trains of waves radiated per second, 18. 

In another experiment made between the “ Monarch ” 

and the Hill of Howth 65 - miles away, with weak coupling, 

and a hill intervening, this empirical formula became 

r _ 0-0364 
b ~ 60 + r 

It would appear it is this constant (60) that Fessenden calls 
the radiation resistance, and which he has reduced to about 
6 ohms. 

Method of Finding best Coupling in Sending Circuits .—The 
following experiment of Duddell and Taylor shows the 



191 


MEASUREMENTS IN 


RADIO-TELEGRAPHY. 


importance of obtaining the best coupling-up of the sending 
circuits. An auto-transformer was used with seventy turns 
of wire in the aerial circuit. The sending and receiving 
circuits having been accurately tuned, signals were sent 
over miles, with the following results :— 


Number of Turns 
of Auto-transformer in 
common to both 
Circuits. 

Current in 
transmitting Aerial 
in Amperes. 

Current in 
receiving Aerial in 
Micro-amperes. 

2 

2*21 

313 

^ 1*5 

2*17 

333 

1 

2*02 

334 

0*5 

1*66 

279 


The Currents in Oscillatory Circuits .—As earlier explained, 
for the greater part of the time that signals are being sent 
there is actually no current flowing in oscillatory circuits. 
When it is flowing it pulsates in opposite directions, so that 
no instrument can be used which takes into account the 
direction of the current; accordingly the heating effect of a 
current on a wire, being independent of the direction, is 
generally utilised in instruments for measuring oscillatory 
currents. 1 

When two or three amperes are measured it is probable 
that the maximum current reaches several hundred amperes, 
and as the current only penetrates the skin of the con¬ 
ductor the current density would momentarily reach several 
hundred thousand amperes per square inch. 

1 The current measured is the square root of the mean current 
squared ; it is generally abbreviated and called the R.M.fS. current. 














192 


RADIO-TELEGRAPHY. 


Use of A mmeter in Subsidiary Circuit. —As a general rule 
all that is required is to measure relative currents; it is 
then often most convenient at the transmitter to place the 
measuring instrument in a subsidiary oscillatory circuit of 
the same oscillation constant and acted on inductively. 
The arrangement is shown in Fig. 13i. in taking measure¬ 
ments the known inductance l 2 is placed at a distance from 
the single turn of inductance Ii, 1 so as to get convenient 

readings on the ammeter A, but it must 
not be placed too near, otherwise confound 
waves are produced. When the variable 
known capacity C is such that either in¬ 
creasing or diminishing it reduces the current 
through A, the oscillation constants are the 
same. It is this arrangement that is used 
for measuring wave-lengths. 

Measuring Instruments used in the Trans¬ 
mitter. —The type of instrument generally 
employed in the sending circuit is a hot-wire ammeter. 
The current heats a fine platinum wire, causing it to sag, 
and the sag is magnified by an arrangement of levers 
and pointer. For radio-telegraph work the platinum wire 
should not be larger than No. 40 S.W.G., or several wires 
of this size, and the same length should be placed in 
parallel. 

Another very sensitive current indicator is the electric 

1 The arrangement of the two inductances would be very like that of 
the receiving transformer, Fig. 150, p. 222. 











MEASUREMENTS IN RADIO-TELEGRAPHY. 193 

thermometer. A wire to be heated by the current is at 
one end of a U-tube partially filled with liquid. The 
aperture at this end can be closed by a cock. The heating 



Fig. 132. 


of the wire causes the air in the tube to expand, driving the 
liquid up the further leg of the U. It is important to 
have the self-induction and resistance of the measuring 


R.T. 


o 























194 


EADIO-TELEGRAPHY. 


V 


0 


instrument sufficiently small, so that it does not sensibly 
alter the wave length or damping. 

The Thermo-galvanometer. —Mr. W. Duddell has designed 
a very sensitive thermo-galvanometer for measuring currents 

in the receiver circuits, which is per¬ 
fectly accurate for high frequency cur¬ 
rents after standardisation by direct 
currents. It consists essentially of a 
resistance of negligible self-induction 
and capacity placed near a thermo¬ 
couple of bismuth and antimony. 1 The 
rise in temperature of the lower junc¬ 
tion of this couple produces a current 
in a loop of wire which is deflected by 
a magnetic field against the torsion of 
a quartz fibre. 

This instrument is illustrated in Fig. 
182 and is shown diagrammatically in 
Fig. 138. 

In the field between the pole-pieces 
N, S (Fig. 133) of a permanent magnet 
Eig. 133. f s suspended by means of a quartz fibre 

Q a single-turn coil or loop of wire L, to the lower ends of 
which is fixed a thermo-couple. This loop is surmounted 


M 

G 

.L 



N 


/ 


Bi \ Is A 


Heater 


1 If the junction of two different metals in an electric circuit be 
heated to a different temperature from the rest of the circuit an 
E.M.F. is set up between them. The two metals which produce 
greatest E.M.F. are bismuth and antimony, giving rather more than 
100 micro-volts per 1° C. 

















MEASUREMENTS IN RADIO-TELEGRAPHY. 


195 


by a glass stem G which carries a mirror M. Below the 
lower junction of the thermo-couple is fixed the heating 
resistance or “ heater,” one end of which is connected to 
the frame of the instrument to avoid electrostatic forces. 
The current to be measured passes through the “ heater,” 
raising its temperature, causing the lower junction of the 
thermo-couple to rise in temperature above the upper, thus 
producing a current round the loop L which is deflected 
by the magnetic field against the torsion of the quartz 
fibre Q. 

The deflections of the instrument are practically propor¬ 
tional to the square of the current when the heater is 
central under the junction. The sensibility of the instru¬ 
ment depends on the resistance of the “ heater ” and on its 
distance from the thermo-junction. The “ heaters ” are 
set up in small protecting cases with contact rings, so that 
they can be interchanged quickly when it is desired to 
greatly alter the sensibility of the instrument. 

An adjusting-screw F (Fig. 132) is also provided so that 
the distance between the “ heater ” and thermo-junction 
can be varied, and by this means small changes in the 
sensibility can be made without altering the “heater” or 
changing the shunts in use for the experiment. 

The base of the instrument is fitted with levelling screws 
and levels. Fig. 132 shows the heavy metal plate E which 
protects the couple removed and standing on the base of 
the instrument. A stout mahogany cover (not shown in 
the illustration) protects the instrument from dust and 

o 2 


196 


RADIO-TELEGRAPHY. 


heat radiation. The mirror M (Fig. 133) is plane, but the 
instrument is fitted with a lens which gives an image on 
the scale at a distance of one metre when used with the 
ordinary galvanometer lamp and scale. 

The following table shows the approximate sensibility of 
the instrument with heaters of different resistances. 


Table of approximate Sensibilities. Scale distance 

One Metre. 


Resistance of 
Heater. 

Current to give 
250 mm. 
Deflection. 

Current to give 
10 mm. 
Deflection. 

P.D. to give 
250 mm. 
Deflection. 

P.D. to give 10 mm. 
Deflection. 

Ohms. 

Micro-amperes. 

Micro-amperes. 

Millivolts. 

Millivolts. 

About 1,000 

110 

22 

110 

22 


9 9 

400 

175 

35 

70 

14 



100 

350 

70 

35 

h? 

J 


9 9 

40 

550 

110 

22 

4-4 

( Heater close to 
j junction. 

9 9 

10 

1,100 

220 

11 

2-2 

1 9 

4 

1,750 

350 

7 

1-4 


9 9 

1 

3,500 

700 

3*5 

0-7 J 

( Heater lowered 

9 9 

1 

10,000 

2,000 

10 

2-0 

! away from junc- 
. tion. 


The above are the ordinary resistances of the heaters 
supplied for use with the instrument; but any intermediate 
value can be supplied by the makers. The heaters from 
40 ohms downwards are metal wires and are adjusted to 
within ±15 per cent. Those above 40 ohms consist of a 
deposit of platinum on quartz and are adjusted to within 
± 25 per cent, of the values in above table. 

The instruments generally attain their full deflection to 
within 1 part in 500 after ten seconds. 

The Bolometer. —C. Tissot has successfully employed a 
















MEASUREMENTS IN RADIO-TELEGRAPHY. 


197 


bolometer for measuring the current in a receiver circuit. 
A bolometer consists essentially of two line metal wires 
placed as two arms of a A\heatstone bridge. The bridge is 
balanced, and the current to be measured is sent through 
one arm, raising its temperature and resistance so that 
balance has to be obtained again. The arrangement has 
to be calibrated with direct currents as in the case of the 
thermo - galvanometer. One method of measuring the 
current is shown in Fig. 134. A B are two arms of the 
bridge ; the other two arms 
G F consist of fine wires, 

1*5 cm. long and 0*01 mm. 
diameter, with special iron¬ 
less choking coils C D 
placed between. Finally a 
very sensitive galvanometer 
and battery are connected 
as shown, and one of the 
fine wires is placed in the receiving circuit. The impor¬ 
tant precautions to be taken are to localise the received 
current in one of the fine wires to prevent irregular 
heating from outside sources, and to prevent the heating 
of the one wire affecting the other. Tissot with this 
arrangement was able to obtain deflections of 10 mm. on 
a scale 1 metre away with 100 micro-amperes. Later experi¬ 
menters have obtained greater sensibility by using Fes¬ 
senden’s barretter with wires 1*5 mm. long and 0*002 mm. 
diameter. 






















198 


RADIO-TELEGRAPHY. 


The High Frequency Dynamometer. —G. Pierce has used 
an instrument on the dynamometer principle for measuring 
relative currents. It consists of a small coil about 8 mm. 
diameter, with 30 turns of 0*1 mm. wire. This coil is in 
series with the condenser circuit of the receiving station. 
Immediately in front of the coil is hung a plane glass 
mirror 3 mm. diameter, bached by a thin disc of silver, and 
making an angle of 45° with the plane of the coil, the 
distance being regulated by a micrometer. Oscillations in 
the coil induce oscillations in the disc, increasing the angle 
between them. The deflections are read by means of a 
telescope and scale, and it has been found that the deflection 
is proportional to the square of the current. G. Pierce 
found with this instrument that he could directly compare 
quantities of energy that were in the ratio of 1 to 20,000. 

Wave Measurement .—It has been shown how relative 
currents can be measured by using an auxiliary circuit 
containing an ammeter, and having the same oscillation 
constant as the main circuit. If the self-induction and 
capacity of this auxiliary circuit be known, we have a direct 
method of measuring the frequency of the vibration and 
consequent wave-length of the radiations. J. Zenneck was 
the first to make use of this arrangement, and several prac¬ 
tical instruments have been made on the principle. 

Die Gesellschaft fur Drahtlose Telegraphie manufacture 
an instrument designed by Donitz, illustrated in Fig. 135, 
which they call an ondameter. 

The variable condenser consists of two parallel sets of 


MEASUREMENTS IN RADIO-TELEGRAPHY. 


199 


plates, one of which is fixed, whilst the other can be rotated 
so that more or less of the surface is between the fixed 
plates. To obtain greater capacity the whole is immersed 
in oil. One of three coils of inductance can be used, 
depending on the wave-length to be measured. One of 



Fig. 135. 

these is shown in position to the right of the condensei, 
and to the left may be seen the electric thermometei, and 
as the heated wire has varying resistance it is not in direct 
circuit, but is acted on inductively by means of a miniature 
transformer with a primary of one turn. This instrument 
can be used for measuring wave-lengths of from 100 to 

1,200 metres. 






200 


RADIO-TELEGRAPHY. 


The type of instrument used in the Marconi system was 
designed by Professor Fleming, and is called by him a 
cymometer. A plan and elevation are given in Fig. 136. 
The makers describe the principle of the instrument as 
follows:— 

“ It consists of a sliding tubular condenser formed of two 
brass tubes, separated by an ebonite tube. The outer tube 



Eig. 136. 


can be moved by a handle A, and an index pointer P moves 
with it over a divided scale SS. Parallel with the condenser 
is an inductance coil HH, consisting of a bare copper wire, 
wound on an ebonite tube, and from the outer tube of the 
condenser 0, a pin I projects, which carries a half collar K 
resting on the inductance coil. The circuit of the con¬ 
denser and inductance is completed by a copper bar L L of 
square section. With the instrument is supplied a vacuum- 
tube Y, filled with rarefied neon, attached to two small hooks 























































































































































































MEASUREMENTS IN RADIO-TELEGRAPHY. 


201 


placed on the ends of copper wires, which are respectively in 
connexion with the outer and inner tubes of the condenser. 

The instrument is employed in the following manner :— 
Place the cymometer so that the copper bar L L is parallel 
with, and close to, any straight portion of the circuit in 
which electric oscillations are taking place. Then fix the 
vacuum-tube to the two small hooks in connexion with the 
terminals X Y, and screw the ebonite handle into the thick 
collar K of the outer tube of the sliding condenser. Move 
the handle, thus sliding the outer tube of the condenser 
along, until the vacuum-tube glows most brightly. Then 
the end of the index slip P will indicate on the lowest of 
the four scales the number of oscillations in one millionth 
of a second. Thus, su|)pose it reads 3*5, this indicates that 
the frequency of the oscillation is 3*5 millions. Also the 
top scale reading indicates the oscillation constant of the 
circuit being tested, viz., the square-root of the product of 
the capacity in microfarads and inductance in centimetres 
of the circuit. If then we know either the inductance or 
the capacity of that circuit we can determine the second 
quantity. The range of the oscillation constant for the 
instrument illustrated is from 0 to 12.” 

To measure the wave-length of an aerial circuit with the 
cymometer it is placed several inches from the oscillatory 
circuit at the antinode of current, and with the copper bar 
parallel to the aerial wire ; the handle of the instrument is 
then moved till the vacuum-tube glows most brightly, when 
the wave-length can be read. 


202 


RADIO-TELEGRAPHY. 


For rough work Dio Gesellschaft fur Drahtlose Tologiaphie 
make an instrument invented by Professor Slaby called 
a Multiplicator. A long solenoid of wire, whose length 
can be adjusted, is connected to the oscillatory circuit, the 
free end acting on a tube containing platino-cyanide of 
barium. When the oscillation constant of the solenoid 
is the same as that of the circuit to be measured the tube 
becomes most luminous. Fig. 187 shows a box containing 



Fig. K37. 

% 

three of these solenoids. With this instrument Slaby found 
that if held six feet from the earth the wave-length of the 
rod was increased 8 per cent., due to capacity ; but at 
fifteen feet it was inappreciable. He further found that the 
inductive influence of conductors was about half the capacity 
influence acting in the opposite way. 

In the case of measuring the wave length of an open 
aerial circuit, say with a Donitz wavemeter, the arrange¬ 
ment of apparatus is as in Fig. 181. The transmitting key 
is held down and the capacity of the wavemeter altered till 
















MEASUREMENTS IN RADIO-TELEGRAPITY. 


203 


the largest reading is obtained on the ammeter. To bring 
an open circuit to the same frequency as a closed circuit two 
methods may be adopted, either (1) an ammeter may be placed 
directly in the open circuit and the induction coil circuit 
closed; then, by altering the inductance of the open 
circuit, the largest reading of the ammeter may be obtained, 
and the two circuits are in tune. It must be remembered 
that if the coupling be close two maxima are obtained. The 
second method (2), is to place the wave- 
meter in the open circuit and complete 
the closed circuit. In measuring the wave¬ 
length of a secondary receiving circuit it 
is best, when the coupling is very close, to 
use a very small induction-coil with spark- 
gap G in the aerial circuit, to avoid break¬ 
ing down the receiving transformer R, 
placing the ammeter or wavemeter W 
(see Fig. 138) in the secondary. 

If sufficient energy be available, the tuning at the receiving 
end can be accomplished with instruments of the Donitz 
or Fleming tyjDe by replacing the electric thermometer or 
vacuum tube by a thermo-galvanometer or bolometer. 

If, however, the inductance of the secondary winding of 
the receiving transformer be known, and a standard variable 
condenser be available, it is easy to measure the wave¬ 
length of any distant station. The method is shown in 
Fig. 139. The secondary I of the receiving transformer 
must be capable of being shifted relatively to the primary 
















204 


RADIO-TELEGRAPHY. 


J ; the detector D, patentiometer P, and telephone receiver 
T form a shunt to the variable known capacity K. To 
measure the wave-length of a distant station, the two 
receiving circuits are brought into tune by altering the 
inductance L and the capacity K. The secondary of the 
receiving transformer is then moved away from the primary 

until the sound in the telephone 
receiver is just audible. When 
the receiving station is in tune 
with the station to be measured, if 
the slightest alteration is made to 
the capacity Iv, the signalling ticks 
in the telephone receiver are lost. 
By this method the author has 
measured the wave-lengths of two 
stations sending simultaneously, and whose wave-lengths 
differed only two per cent. 

The Theory of Wave Measurement .—The theory on which 
wave measurements are taken is due to Lord Kelvin. He 
determined that to obtain electrical oscillations in a circuit 
R 2 1 

4~py must be less than where Pt is the resistance to 

oscillatory currents, L the self-induction, and C the capacity 
of the circuit. 

Ihe periodic time T of the vibrations is given by 

m 2 7T 

/I w' 

V L C 4 L 2 






h 


|“\]-AAA/VVWv 


T 


Eig. 139. 
















MEASUREMENTS IN RADIO-TELEGRAPIIY. 


205 


R 2 

In radio-telegraph circuits mac ^ e sufficiently small 

to be neglected, and we have 

T — 2 77 y/ L 0 — 2 7T S' — — 

11 

where s is the oscillation constant, and 

U ~ 2 77 VlTC* 

The wave length in metres A is given by 

, 3 X 10 8 

A = - 

11 

where n is the frequency of the oscillations. 

For practical measurements 

a = 6o vul, 

where C is the capacity of the circuit in microfarads and 
L the inductance in centimetres: 

or A = 60,000 VcTi 

where Li is inductance in millihenrys. 

Resonance Curves. —It is advisable in taking the ■wave¬ 
length to use a measuring instrument in preference to a 
vacuum-tube, as it enables a resonance curve to be qdotted. 
In the case of a sending circuit the resonance curve shows the 
relative vibratory current and consequent energy radiated 
of different w T ave-lengths greater and smaller than that of the 
principal wave-length, and thus indicates the amount which 
the transmitter is likely to interfere with other stations; 
and in the case of the receiving circuit, the resonance curve 
shows the relative vibratory currents received of various 









206 


RADIO-TELEGRAPHY. 


wave-lengths, indicating the likelihood of interference from 
other stations. The resonance curve is best taken with fixed 
inductance in the subsidiary circuit. Commencing with 
small capacity the current is measured; then altering the 
capacity by given amounts successive currents are read. 
In the case of an open circuit, when the results are plotted, 
a curve of a similar nature to Fig. 140 is obtained. 



400 4 20 440 460 480 500 520 540 560 

Wave Length, in Metres. 


Eig. 140. 

Generally the steeper the shape of the curve the more nearly 
is the circuit vibrating to one fundamental. At the peak 
of the curve it is best to take a large number of readings, 
as slight differences in the spark are liable to cause large 
differences in the maximum current readings. 

G. W. Pierce, in taking resonance curves of the receiving 
aerial, has used his dynamometer directly in the circuit and 
altered the receiving capacity. He also used the Cooper- 
Hewitt mercury interrupter instead of spark-gap, on account 
of the constant results obtained, only one reading being 


















MEASUREMENTS IN RADIO-TELEGRAPHY. 


207 


necessary, whereas using a spark-gap it is necessary to take 
the mean of at least five readings. 

Resonance Curves oj Coupled Circuits .—When two circuits 
are coupled the mutual inductance generally causes two 
distinct sets of oscillations. This is clearly illustrated in 



Capacity in Receiving Circuit. 


Fig. 111. 

Fig. 141, giving results obtained by G. W. Pierce taken in a 
receiving circuit with a magnetically coupled sending circuit, 
having an aerial 16 metres long. Each curve represents 
results taken with different lengths of receiving aerial, the 
number against each letter being the height of the aerial 
in metres. From numerous experiments Pierce drew a 























































208 


RADIO-TELEGRAPHY. 


series of these curves, and from the maximum deflections 
he plotted fresh curves with the height of the receiving 
antenna against the receiving capacity, which gave the 
maximum deflection; thus points A, B, C, D and E of Fig. 
141 are shown in Fig. 142 as A', B', C', D', E'. 

It will be seen from these curves, if empirical methods 



Capacity in Receiving Circuit. 

Eig. 142. 


are used, how easy it is to set the receiving circuit in tune 
with one of the weaker oscillations of the transmitter ; and 
it will also be noticed, in the special case considered, that 
with the receiving mast the same height as the sending 
mast, it required almost infinite capacity in the receiver 
circuit to obtain the maximum result of the most powerful 
wave. 

Measurement of Coupling between Two Circuits .—The 







































MEASUREMENTS IN RADIO-TELEGRAPIIY. 


209 


coupling K between two circuits may be defined mathe¬ 
matically by the equation 

_ M 2 
~ L x L 2 ’ 

where Li L 2 is the self-induction of each circuit and M is 
the mutual induction between the circuits. If all the 
magnetic field of force from each circuit were embraced by 
the other circuit we should have 

M 2 = L x L 2 

and K = 1. 

This would be the closest imaginable coupling, and cannot 
be realised. 

In the case of close coupling, taking the resonance curve 
with its two principal wave-lengths, Drude has shown the 
shorter of the two is given by the equation 

Aj = A 0 V 1 — K 

where A 0 is the natural wave-length of each of the circuits 
taken separately. 

The longer is given by 

A 2 = A 0 V 1 + K 

from which 

t- _ A 2 2 — Ap 

1V ~ A 2 2 + A/ 2 ’ 

enabling the coupling K to be calculated from the resonance 
curve. According to Fleming, in the case of magnetic 
coupled circuits, the best results are obtained when the 
coupling circuits is such that 

A 2 — 3 Ai. 


R.T. 


p 






2l() 


RADIO-TELEGRAPHY. 


Damping .—The damping decrement 5 is given by the 
equation 

h = log e t 1 = log e y, etc., 

where Ii, I 2 , I 3 are successive maximum values of current. 



•98 -99 1 1'01 102 

Principal Wave in Metres -f- Ware length. 


Eig. 143. 


For a circuit with resistance to oscillatory currents R, 
capacity C, and self-induction L, 



The governing factor is the resistance. With best shaped 
inductance coils, increasing the number of turns of wire 























MEASUREMENTS IN RADIO-TELEGRAPHY. 


211 


increases the resistance more in proportion, thereby 
increasing the damping. 

The Damping Curve .—Drude has shown that the damping- 
decrement of an oscillatory circuit can be obtained from 
the resonance curve. From this last-named curve the ratio 
of maximum current squared to any other current squared 

(thO * s P^°^ ec ^ a g a i ns t ^ ie i’ a tio of wave-length corre¬ 
sponding with the given current to principal wave-length. 
Thus taking the resonance curve of Fig. 140 the damping 
curve Fig. 143 is obtained. 


The damping decrement h is obtained from the formula 


-J- §2 — 7T 3C 

A 

II 

I 

■ ^ i 

x A. 

Generally §2 the damping decrement 

of the auxiliary 

circuit may be neglected. 

For 

several convenient values 

of y the quotient tt \/-. 

- is given in i 

y 

table below. 

y 

0*95 



A 

13*7 

0*9 

. . . 

... 

9*4 

0-85 

. . . 

... 

7-5 

0*8 

. . . 


6*3 

075 

• • • 

... 

5-5 

0*7 


... 

4-8 


x is measured from the curve and 8 is thus easily calculated. 
Damping of Compound Oscillations .—If h be the damping 

p 2 






212 


RADIO-TELEGRAPHY. 


decrement of a primary sending circuit, and S 2 the decre¬ 
ment of the aerial circuit, then according to Drude the two 
waves radiated have decrements 

-P* _ &i + & 2 __ 

1)1 ~ 2 A x 

-f“ S 2 _ ^0 

1)2 ~ ^ 2 A 2 

where A b A 2 are the forced principal wave-length of the 
circuits due to mutual induction, and A 0 is the natural 
wave-length of each of the circuits. In practice with 

coupled systems the damping of the closed circuit is made 
very small compared with the radiating circuit, and with 
the closest coupling 



where D is decrement of the radiated waves ; that is, under 
the conditions of greatest damping the decrement of the 
radiating circuit is reduced to half the natural decrement. 

Comparison between the Damping of Closed and Open 
Circuits .—This result of Drude is sometimes taken to show 
the advantage of coupled over open systems. What it does 
show is that, when syntonic working is employed, and the 
receiver is properly arranged so as to require a large 
number of tuned impulses, the closest coupled system is far 
superior to the open-circuit single aerial. 

The formula does not admit of a comparison between 
coupled circuits and a system using an aerial loaded with 
capacity such as advocated by Lodge. To take an extreme 
case, the carpet of Lodge might be made of sufficient area 




MEASUREMENTS IN RADIO-TELEGRAPHY. 


213 


to make its capacity equal to that of a good closed circuit; 
and the radiation of the two systems could be made the 
same. The theoretical advantage would then be with the 
carpet aerial, as the damping would be less, due to the 
absence of transformation losses. 

Ohmic Resistance of Wires .—Lord Rayleigh has shown 
that for high frequencies the resistance of a wire of diameter d 
can be calculated from formula 





where R a is resistance of the wire for the alternating 
current, R c the resistance for constant currents, d the dia¬ 
meter of the wire in centimetres, and n the frequency of the 
oscillations; but this formula is only applicable to high 
frequencies and for large wires. 

Number of Oscillations in a Train of Waves .—It has 
been shown how to obtain the damping decrement from the 
resonance curve; the damping decrement 5 is also given 
by the formula 

* , Cl 1 c 2 , c 3 , 

5 = log e = log € ^ = log e ^ etc., 
l 2 l 3 Li 

where Ci C 2 C 3 are successive maximum amplitudes of current 
which, however, cannot be directly measured. 

For the number of complete oscillations N, in the case 
of natural vibrations, before they are reduced to 1 per 
cent, of their initial amplitude, Fleming gives the following 
useful formula:— 


4*606 + 5 




214 


RADIO-TELEGRAPHY. 


In the following 
a few decrements. 


C 

table the ratio of —^ and N are given for 

L2 


8. 

o 2 

x 100. 

Ci 

C 2 ' 

N. 

o-ooi 

99-9 

1-001 

2,300 

0-005 

99-5 

1-005 

1,150 

o-oi 

99-0 

1-01 

230 

0-05 

95-1 

1-05 

115 

0-1 

90-5 

1-10 

23 

0 0 

60-7 

1-65 

5 

10 

36-8 

2-72 

3 


Number of Trains of Waves per Second. —A convenient 
method of measuring the number of trains of waves per 
second is that due to Fleming. A seconds pendulum 
alternately makes and breaks the induction coil circuit for 
periods of one second, and operating at the same time a 
circuit which causes a tape to travel through the spark- 
gap. For every train of waves the tape is pierced, thus 
enabling the number to be counted. 













CHAPTER XI. 


THE EXPERIMENTAL STATION AT ELMERS END-LODGE- 

MUIRHEAD SYSTEM. 

The Lodge-Muirhead method of radiating energy from 
the oscillator is gradually becoming more and more near 
to the ideal of Sir Oliver Lodge, 
as formulated in his patents of 
1897 (see Eig. 144), and has thus 
developed on completely different 
lines from the methods of Mar¬ 
coni, Braun, De Forest, and 
Fessenden in two important 
respects. Whilst the latter in¬ 
ventors have aimed at obtain¬ 
ing 

(1) A good radiating circuit 
coupled to a slightly damped 
condenser circuit, and 

(2) As efficient as possible a connexion of the radiating 
circuit to the earth by conduction or induction, 

It has been the object of Lodge 

(1) To use only one oscillatory transmitting circuit of 
an intermediate character, and 



Fig. 144. 
























RADIO-TELEGRAPHY. 


210 

(2) To remove this oscillatory circuit as far as possible 
from the influence of the earth. 

To obtain the most perfect syntony, Dr. Alexander Muir- 
head has recently found that the best position for the lower 
aerial is such that its capacity is a minimum, and that if it be 
raised higher the radiating power is diminished. Using this 
method the Lodge-Muirhead Syndicate have found it possible 
to maintain communication up to a distance of 60 miles 
over hilly country with the two capacity areas at each 
station only 30 feet apart, and the transmitting energy not 
exceeding 400 watts. 

The sharpness of tuning which can be obtained is indicated 
by the following experiment, which was carried out for 
purposes of demonstration. In this experiment the author 
is informed that recorded communication could be main¬ 
tained with complete success between the Lodge-Muirhead 
radio-telegraph station at Elmers End and Hythe, a distance 
of 58 miles over land, notwithstanding the fact that 
the powerful Dover station within miles of Hythe 
was trying to interfere, and all the usual signalling work 
of the shipping in the channel was going on. It was also 
shown that the instruments at Hythe might be adjusted to 
within about 6 per cent, of the wave-length at the Dover 
station before any disturbing indications were received on 
the tape. The aerial at Elmers End was 10,000 square 
feet and 62 feet high, with the lower capacity raised 12 feet 
above the ground. At Hythe the aerial was 78 feet square 
and 82 feet high, with the lower capacity raised 20 feet, 


THE EXPERIMENTAL STATION AT ELMERS END. 217 


and the transmitting energy was not allowed to exceed 
500 watts. The Dover station had an aerial 180 feet high. 
To obtain these results the receiver was tuned by a Duddell 
thermo-galvanometer to give the largest reading on the 



instrument; then the receiving circuits being still kept in 
tune with the sender, the detector was gradually made more 
and more insensitive, until it would only respond to waves 
within about 5 per cent, of the principal wave. 

The apparatus is manufactured by Messrs. Muirhead & Co. 










218 


RADIO-TELEGRAPHY 




















THE EXPERIMENTAL STATION AT ELMERS END. 219 


Alternators of the type shown in Fig. 145 are made in various 
sizes, with outputs of from 250 to 2,000 watts respectively. 
The periodicity used is 200 ; this is higher than in most 
systems, in which fifty or sixty cycles per second are 
generally employed, but it must be remembered the 
capacity to he charged is smaller than in the case of a 
coupled system, so it is more advantageous to employ a 
large number of discharges with oscillations of smaller 
maximum amplitude. 

The transformers are now made of the open magnetic 
type, giving them the appearance of induction-coils. The 
secondaries are wound in units of 250 watts; thus the 
secondary of a transformer taking 750 watts in the primary 
is made up of three small units in series placed end-on. 
The primary of a 500 watt transformer is wound to take 8 
to 12 amperes at 120 volts, the power factor 1 being about 0’3. 

Fig. 14G shows the arrangement of apparatus at Elmers 
End. The ammeter and voltmeter are at the top of the 
switchboard. At the bottom are the main switch and two 
swatches for regulating the current through the field coils 
of exciter and alternator. In the centre are tv T o choking- 
coils to regulate the current given to the primary of the 
transformer, which is at the back of the table. Above the 
transformer is the multiple spark-gap enclosed in a felt 


The 


factor is the ratio 


watts 


Eor constant 


power io uuu ict-— . 

r aujperes X volts 

current this ratio is always unity. In case of alternating currents 

it is always less than unity, due to difference of phase between pressure 

and current. 



220 


RADIO-TELEGRAPHY. 


lined box, and having artificially cooled spark-knobs. To 
the left of the table is the plugging arrangement for altering 
the inductance in the oscillatory circuit; next to it is the 


fcb 

• i—« 

Ph 










THE EXPERIMENTAL STATION AT ELMERS END. 221 

transmitting key with receiving arrangements to the right. 
Behind the receiver is the plug-board for altering the 
inductance in the secondary receiving circuit; but in the 



Eig. 148. 

latest practice the receiving transformer with adjustable 
coupling (Fig. 150) is used. 

The receiving apparatus is shown in greater detail in 
Fig. 147. To the left is the syphon recorder; to the right is 
the clockwork which drives the coherer wheel, and an inter¬ 
rupter in the telephone circuit; it at the same time moves 
forward the recording tape. The coherer may be seen with 




222 


RADIO-TELEGRAPHY. 


cover removed, but the interrupter is at the far side of the 
clockwork. In front of the recorder are the buzzer for 


testing the coherer and the potentiometer switch, 
right are the change-over switch from “ send ” to “ 


To the 
receive,” 


/VWVWVVWW — 



Eig. 149. 

























































THE EXPERIMENTAL STATION AT ELMERS END. 223 


and a small adjustable condenser with a maximum capacity 
of about 2 centimetres placed in parallel with the coherer. 

Two types of receiving transformer are used. Fig. 148 
illustrates one form which has considerable inductance in 
the secondary and a fixed coupling. In front are a number 
of plug connexions arranged as shown diagrammatically in 
Fig. 149. These enable the inductance to be altered and 



the idle turns short-circuited. The other type is depicted 
in Fig. 150; this has only a few turns of inductance, and the 
circuit is brought into tune by means of the adjustable con¬ 
denser to the left, this condenser being placed as a shunt to the 
coherer and in parallel with the small condenser already men¬ 
tioned. The coupling can be altered by sliding the primary 
winding nearer to or further from the secondary winding. 
The complete connexions of the station are shown in 1 ig. 151. 

To the left are the low tension power circuits, which supply 
the transformer T for charging the oscillator, consisting of 


























224 


RADIO-TELEGRAPHY. 


the aerial and lower capacities A and L in series with the 
multiple spark-gap G and the variable inductance I. To 
receive, a plug is removed from D to E, and the primary of 
the receiving transformer takes the place of the spark-gaps. 
The adjustable secondary S with coherer C and capacities 
Ki K 2 form the subsidiary receiving circuit. K 2 is suffi¬ 
ciently large compared with K x so as not to decrease the 
capacity of the circuit, and is solely for the purpose of 
preventing oscillatory currents from flowing through the 
recorder B and the telephone with its interrupter B. The 



AA 


Fig 152 


buzzer circuit for testing the coherer is shown to the 
extreme right. 

The author is informed that with this arrangement, 
using 350watts at the transmitter, it is possible to maintain 
communication up to distances of from 300 to 350 miles 
over sea, with a space of 110 feet between the capacity 
areas, and that it is also possible to accomplish diplex 
signalling from one set of masts radiating waves whose 
principal wave-length differ only 2 per cent., the signals 
being received simultaneously by means of a single aerial. 

Specimens of two sets of tape thus received are shown in 
Fig. 152. 






CHAPTER XII. 

RADIO-TELEGRAPH STATION AT NAUEN—TELEFUNKEN SYSTEM. 

Die Gesellscbaft fur drahtlose Telegrapliie have kindly 
furnished particulars of their radio-telegraph station com¬ 
pleted in 1906 at Nauen, about 12 miles north-west of 
Berlin. This station can communicate either to Rigi 
Scheidegg, in Switzerland, or St. Petersburg, 845 miles 
away, and messages have been received by ships 2,300 miles 
off. It is worked by two men, a stoker and a telegraph 
operator. 

The aerial arrangements are very complete. The antenna 
is supported by a steel lattice tower (Fig. 153) of triangular 
section; the girders join at the bottom in a cast steel 
sphere which rests on a socket. The pressure is taken 
through a layer of marble which insulates the tower from 
the concrete foundation. This tower is 300 feet in height, 
with 12 feet sides. A platform at the top is reached by 
steps, and there is a second platform 225 feet up, from 
which the guys radiate. These are three in number; they 
consist of steel bars several yards long, connected together 
by links, and anchored about 600 feet from the foot of the 
tower. The guys are insulated from the tower and anchors, 
oil insulators being used at the top, as the surgings in the 


R.T. 


Q 



Fig. 153, 














EADIO-TELEGEAPH STATION AT NAUEN. 


227 


guys sometimes enable sparks of 40 inches to be taken 
from them. 

The umbrella form of the antenna is clearly shown in 
Fig. 154. It consists of six segments arranged so that those 
opposite counterbalance each other ; the raising and lowering 
is performed from the top platform over pulleys. The 
surface covered by the antenna is about 650,000 square 
feet. From the tower radiate six phosphor-bronze wires 
which gradually increase to 162 in number towards the 



circumference. The outer edge is held in position by hemp 
cords connected through porcelain insulators. The antenna 
is not insulated from the tower, which thus forms part of 
the oscillatory circuit, but it is supplemented by 154 wires 
in the form of six grids held together by wooden battens. 

From the tower radiate 108 iron wires arranged fanwise, 
which gradually branch into 324 wires. These wires are 
buried and form the earth connexion, covering an area of 
rather more than 30 acres. 

The station buildings, not including engine room, cover 
about 1,000 square feet; the room containing the condensers, 
spark-gap, and other high tension mechanism is on the 

Q 2 







228 


RADIO-TELEGRAPHY 


first floor; all the other apparatus and sleeping accommoda¬ 
tion is on the ground floor. 

For power equipment a 86 h.p. steam engine \ drives 































RADIO-TELEGRAPH STATION AT NAUEN. 


229 


a 25 k.w. 50-periodicity alternator for charging the 
primary oscillatory circuit through four transformers, 



































































































































230 


RADIO-TELEGRAPHY. 


whose primary windings are in series and the secondary 
windings in parallel. 



Eig. 157. 
































BADIO-TELEGBAPII STATION AT NAUEN. 


2 ‘ 6 \ 


The apparatus comprising the primary oscillatory circuit 
is shown in Fig. 155. The battery of three sets of 120 jars 
has a capacity of 400 microfarads. The inductance placed 
in between the condensers as shown in the illustration con¬ 
sists of a spiral of silver-plated tubing. To the right of the 
condensers may be seen the spark-gaps; these are ring- 
shaped, and four are placed in series. Two spare gaps are 
ready in case of need. To the extreme right are two 
choking coils, placed to protect the secondary winding of 
the transformer. In front of the battery of condensers is 
the operator measuring the wave-length of the circuit, and 
on the wall may be seen a portion of the gear for switching 
over from transmitting to receiving. This switch either 
connects the antenna to the transmitting circuits at A or 
to the receiving circuits at B (Fig. 156). Changing from 
“send” to “receive” also operates the cut-out C, which 
prevents the condensers being charged by mistake. The 
transmitting is done by a Morse key K on the operating 
table, which works a relay B. It will further be seen from 
the figure that the aerial wires are earthed through choking- 
coils D, where they enter both the high tension and the 
receiving rooms with a spark bye-pass, and it will be also 
noticed that both the alternator and exciter, besides the 
usual condenser to earth protection, are shunted by small 
spark-gaps. 

The receiving apparatus is shown in Fig. 157- 


CHAPTER XIII. 


THE RADIO-TELEGRAPH STATION AT LYNGBY — POULSEN SYSTEM. 

Reference has been made in previous chapters 1 to 
Poulsen’s application of the musical arc to obtain undamped 
waves. This system is being worked in England by the 
Amalgamated Radio-Telegraph Company (formerly the De 
Forest Company), who have kindly furnished the informa¬ 
tion in this chapter. 

The essential difference as far as practical results go is 
that with the Poulsen arc a signal of a single dot is obtained 
at the receiving end by about 5,000 small oscillations at the 
transmitter, with a working pressure of from 400 to 500 
volts, instead of from 1 to 100 vibrations of larger 
amplitude, and a pressure of from 10,000 to 100,000 volts. 
The company claim that by this means a 10 k.w. generator 
only is necessary for signalling 1,000 miles, and up to the 
present, utilising the same aerial, three separate messages 
can be received at the same time with wave-lengths differing 
1 per cent., thus showing the undoubted advantage of 
being able to eliminate all outside disturbances. 

Masts of impregnated wood, made of 10 feet lengths, are 
recommended for the aerial, and two separate antennae; 

1 See pages. 88, 141 and 1(30, 


RADIO-TELEGRAPH STATION AT LYNGBY. 


233 


one of these is made suitable for receiving waves of 
from 600 to 2,000 metres over distances more than 300 
miles ; and the other, waves of 300 to 1,000 metres over 
shorter distances ; whilst the shape of the antenna depends 
on local conditions. For a 300 mile circuit two masts of 
130 feet, or one of 180 feet, are used. The earth connexion 
generally consists of about 20 rays 160 to 330 feet in length, 
buried about one foot below the surface; but in permanently 
damp soil earth plates of from 100 to 200 square feet are 
used. 

Poulsen described the progress made up till November, 
1906, in the following words: u Tlie following facts illus¬ 
trate the quick progress of the experiments. In June, 1905, 
our first sending station at Lyngby, near Copenhagen, was 
ready for use. After some small preliminary experiments, 
we established a receiving station at a distance of about 
nine miles, and were able to receive signals there after 
having experimented for a couple of days. After that a 
somewhat larger receiving station was built at a distance 
of about 27 miles; with this we had communication 
the same day the installation was finished. Then, in 
order to experiment across the whole width of Denmark, 
we established a station at Esbjerg. There we also obtained 
communication the same day the installation was completed. 
The distance is here nearly 180 miles, and the waves chiefly 
travel across dry land. The signals are plainly intelligible 
in the telephone, even when the consumption of energy 
is only about 800 watts, and the energy radiated about 100 


234 


RADIO-TELEGRAPHY. 


watts; the difference of potential between the antenna and 
earth is then only a few thousand volts. The wave-lengths 
for these experiments lay between 700 and 1,000 metres. 
Later on, by strengthening the magnetic field of the arc, we 
have, with a wave-length of 882 metres, obtained a radiating 
power of about 400 watts; which, of course, produced a 
powerful effect at Esbjerg. 

“On one occasion the Esbjerg station was fitted up to 
receive signals transmitted by spark-telegraphy. The result 
was most instructive. Instead of the uninterrupted com¬ 
munication formerly obtained, the receiver gave out an 
inextricable jumble of English and German signals from 
land and ship stations; and, in addition to that hopeless 
entanglement, the situation was complicated by the constant 
interposition of atmospheric discharges. On reverting to 
our own methods, the conditions became entirely changed. 
Our communication with Lyngby was instantly restored, 
without the slightest disturbance from extraneous sources. 

“ Recently, with a power of about 1 k.w., perfect 
communication during day and night has been established 
between Copenhagen and North Shields, a distance of 580 
miles, 150 of which are overland, with a height of mast of 
only 100 feet.” 

More recently a station has been erected in North Devon, 
which can communicate with Lyngby 860 miles away. 

A brief description of the Lyngby station is of interest. 
Two 100-feet masts are employed. The generating plant 
consists of a 5 b.h.p. gas engine, driving two 2 k.w. dynamos 


RADIO-TELEGRAPH STATION AT LYNGBY. 


235 



each giving 16 amps, at 100—130 volts, or 4 amps, at 400 
—600 volts. 

At the lower voltage the dynamo charges a battery of 
accumulators which are joined in groups in parallel, and 
can be discharged all in series through the arc. 


Fig. 15S. 

In Fig. 158 to the left of the table are the switchboards 
controlling the dynamo and accumulator circuits. On the 
table to the extreme left is the arc, which consumes about 
100 litres of coal gas per hour. With the electro-magnets 
to right and left of the arc in circuit, the length of arc is 
3 mm. at 440 volts. In the apparatus illustrated the carbon 
which forms the cathode is 1 inch in diameter and is changed 




















236 


RADIO-TELEGRAPHY. 


every hour, whilst the anode is a copper ring which lasts 
about two months. 

In the centre of the picture is an auto-transformer, which 
in this case is close coupled, the total number of turns of 
wire being 30, of which 12 turns are in the closed arc 
circuit. A close coupling is in fact nearly always employed, 
as it has been found that tuning can be made equally sharp 
with either close or loose coupling. 

In front of the transformer is the transmitting key. At 
Lyngby the key does not make and break the current 
through the arc, but connects and disconnects the antennae 
from the transmitter. 

To the extreme right is the adjustable condenser, which 
consists of a number of semi-circular plates fixed one above 
the other, horizontally and in parallel. An equal number of 
similar ones are mounted on a rotating centre-piece in such 
a way that when the milled head of the centre-piece is 
turned, these plates are carried in between the fixed ones, 
which are mounted with sufficient space between each to 
allow room for the movable plates. 

On the same table 1 is the receiving apparatus. To the 
extreme right is the receiving transformer. The primary, 
which consists of 24 turns of copper wire, is separated from 
the secondary 33 inches, for permanent signalling from 200 
miles away; but the distance between the coils can be 
shortened if required. The adjustable condenser and fixed 
condenser are on the wall. The secondary winding consists 

1 Fig. 159 is a continuation of Fig. 158. 


RADIO-TELEGRAPH STATION AT LYNGBY. 


237 


of 10 turns, and is connected to the adjustable air condenser 
of about 0*001 mf. To the left is the “ ticker,” which is in 
this instance of the vibrator type, and in front is a 0*2 mf. 
block condenser in parallel with the telephone. 

No special detector is used in this station, except for 



Fig. 159. 


experimental work, the breaking of the currents in the 
oscillating circuit causing the tick in the telephone receiver. 
The size of the apparatus may be judged from the operating 
table, which is about 3 feet 6 inches by 3 feet. 

The permanent inductance in circuit is below the table 
and is not shown. 












238 


RADIO-TELEGRAPHY. 


The connexions used at this station are shown in 
Figs. 160, 161. 

The dynamo D supplies current through the resistance It 
and distributing coils S to the arc P, the closed oscillatory 
circuit being coupled by auto-transformers and variable 
capacity C. The primary receiver has fixed condenser K, 
variable condenser C, and transformer winding in parallel. 
In the secondary circuit the block condenser B is in parallel 
with the telephone receiver and in series with the ticker T. 




Several special features of the system might be mentioned. 
The same inductances can be used both for sending and 
receiving, and the primary windings of the receiving trans¬ 
former may be left permanently connected to the aerial. 

The variable inductances consist of two coils of wire, 
having a common centre ; one is fixed, and the other is 
capable of rotation, so that the self-induction can be altered 
without adding to the resistance of the circuit, and it is 
claimed that the normal wave-length can thus be increased 
fivefold. 




































RADIO-TELEGRAPH STATION AT LYNGBY. 


239 


In the latest apparatus instead of changing the carbon or 
cutting it whilst rotating, the arc is made to revolve round 
the carbon. If coal gas is not available a special steel 
generator may be used which holds 2 lbs. of calcium 
hydride. The addition of water produces about 1,000 litres 
of hydrogen gas, which is sufficient for the arc for ten hours. 
The latest mechanism of the receiver consists of the ticker, 
with its two fine-crossed metal wires, vibrating by means 
of clockwork so as first to accumulate energy in the oscilla¬ 
tory circuit before the telephone circuit is completed. If 
preferred the energy may be shunted through a special 
recorder, said to be capable of taking one hundred words 
a minute. 

More recently Electrical Engineering has described 
the latest Poulsen station near Tralee. Three wooden 
masts, each 860 feet high, form a triangle round which nine 
more masts each 70 feet high, are arranged, the diameter of 
the circle being 2,000 feet. The plant is arranged to radiate 
10 to 15 kilowatts with a wave-length of about 8,000 metres. 
The transmitting key directs the energy from the power 
plant from a non-oscillating to an oscillating circuit without 
breaking the current. 

The damping decrement of the closed condenser induct¬ 
ance circuit has been measured as 0'003 inches; the con¬ 
densers are two in number and formed of metal sheets 
separated by air ; each condenser has a capacity of 24,000 
centimetres and occupies a space of 30 cubic feet. The 
ticker receiver is used. 


CHAPTER XIY. 


PORTABLE STATIONS. 

The liability of the field telegraph being cut in time of 
war has led to considerable experimenting on the part of 
the army authorities of the leading Powers to obtain a 
portable and reliable radio-telegraph station, suitable for 
working over a distance of a few miles. Several of the 
systems are here briefly described. 

The Lodge-Muirhead System .—The Lodge-Muirhead 
Syndicate use a collapsible steel mast 50 feet high and 
weighing 62 lbs. The umbrella-shaped aerial and insulated 
lower capacity are clearly shown in Fig. 162. The station 
can be erected in 20 minutes by four men, and it covers a 
space of 60 yards square. The dynamo, which is driven by a 
bicycle arrangement, gives from 60 to 80 watts at 15 volts, 
when worked by one man ; it weighs with driving bicycle 
72 lbs. The sending and receiving apparatus (Figs. 168, 164) 
are mounted in two teak boxes. In Fig. 163 the induction 
coil to the left, Lodge valves in the centre, and multiple 
spark-gap to the right in the lower box, with key fitted on 
the door, are clearly shown. Each of these boxes weigh 
72 lbs., making a total weight of 268 lbs., which can be 
carried by three mules. The nominal range is 100 miles over 


PORTABLE STATIONS. 


241 



sea or 30 to 40 miles over land. To reduce the weight of the 
induction coil, the Lodge-Muirhead valve is employed, so 
that it takes several breaks of the secondary to fully charge 


R.T. 


R 














242 


RADIO-TELEGRAPHY. 


the aerial, thus slightly decreasing the rate of transmission 
to about twenty words a minute. The notched type of wheel- 
coherer is used with a telephone in the receiver circuit. 



Fig. 163. 

[Reproduced from Electrical Engineering of May 23, 1907, by permission of the 

Proprietors.] 

Another transport set for shorter distances, as supplied to 
the Horse Guards, is shown in Fig. 165. It will be seen the 
aerial post is fixed to the cart. The two masts behind are 
those of a fixed station. 

The Marconi System .—The Marconi Company make three 





























PORTABLE STATIONS. 


243 


standard sets. The smallest weighs complete with tent, 
packing cases and saddles, 425 lbs. for mule transport, and 
is suitable for a range of 15 miles over land. The next size 



Pig. 164. 

[Reproduced from Electrical Engineering of May, 23, 1907, by permission of the 

Proprietors. ] 

station weighs 350 lbs., to be carried in a two-wheeled cart, 
and covers 21 miles. These stations can be erected in five 
minutes by six men and one non-commissioned officer. 
Two masts are required, which for the smaller range are 
15 feet and 25 feet, and for the other are each 30 feet high. 

r 2 









244 


RADIO-TELEGRAPHY. 



Fig. 165. 
















PORTABLE STATIONS. 


245 


All are made in 5 feet sections for transport. The aerial 
consists of two horizontal wires 400 feet long, kept 5 feet 
apart; when not in use it is rolled on a drum. An induc¬ 
tive earth is employed consisting of copper gauze about 
3 feet wide and 25 feet long. In the case of the smaller 
set the alternator gives 150 watts, and is driven by three 
men, whilst the next size is fitted with an alternator giving 
300 watts, and requires four to six men to drive it. Both 
stations are for directive working. When first erected the 
station, to be communicated with, may have to be located. 
This is done by first temporarily fixing one mast. A man 
holds a guy wire to support it, whilst a second man moves 
round the pole, carrying the far end of the aerial wire at 
the top of a short pole, and the direction of the station is 
known when the signals received are loudest. 

With the most powerful set a distance of 60 miles 
can be covered. The apparatus weighs 1,350 lbs., to be 
carried by a two-wheeled and four-wheeled cart. The 
aerial consists of four horizontal wires, each 450 feet long, 
supported on five masts 50 feet high. Power is supplied 
by a 2 h.p. petrol engine driving a 1 k.w. alternator. For 
greatest speed fifteen men and two non-commissioned 
officers are required, so as to get the station ready for work¬ 
ing within half-an-hour. In all the stations the magnetic 
detector is used for receiving. 

Telefunken System.— Die Gesellschaft fur drahtlose 
Telegraphie use a mast 45 feet high divided into eight 
parts. The six aerial wires are in the form of an umbrella, 


246 


KADIO-TELEGrKAPHY 



each being 75 feet long, whilst the six earth wires, placed 
3 feet from the ground, are each 120 feet long. One man 
drives the dynamo, which gives one ampere at 45 volts. 







PORTABLE STATIONS 


247 



The ordinary distance of signalling is from 15 to 20 miles, 
but when the wind is sufficiently high kites may be used, 
increasing the distance to about 80 miles. An auto-trans- 





















248 


RADIO-TELEGRAPHY. 


former is used to couple the closed circuit to the aerial. 
The length of spark is from 4 to 5 millimetres, and the 
wave-length is 364 metres. For receiving, the electrolytic 
detector is employed, and waves 5 per cent, different from 
the principal can be shut out. The weight of the apparatus 
is about 440 lbs. It can be carried in a cart, on four mules, 
or over very rough ground by ten men. A station takes 
fifteen minutes to erect with five men. Fig. 166 shows the 
arrangement of the tent and apparatus. The method of 
insulating the mast and earth capacity are clearly shown. 
Just by the mast on two sticks is the variable inductance. 
One man is seen working the dynamo, whilst a second is 
signalling. Fig. 167 illustrates method of packing the mast 
at the side of the transport cart. 

Poulsen System .—This differs essentially from the three 
others described in that it uses the musical arc in hydrogen 
in place of the spark-gap. The Amalgamated Radio-Tele¬ 
graph Company makes a set on this principle for 40 to 50 
miles over flat land. A 4 h.p. four-cylinder benzine motor 
drives a dynamo giving seven to eight amperes at 250 volts, 
but a hand dynamo may be used requiring six to eight men 
to drive it. The aerial mast is 80 feet high, and is made 
of eight steel tubes 10 feet long, resting on an insulated 
plate. It is guyed by steel wires, and takes about ten 
minutes to erect. Bamboo masts are recommended for 
the tropics when they can be obtained on the spot. The 
apparatus weighs about 410 lbs., and requires eight men or 
three pack animals for transport. 


CHAPTER XV. 


RADIO-TELEPHONY. 

Rukmer's Discovery .—The problem of communication 
by means of radio-telephony bears the same relation to 
radio-telegraphy that telephony bears to telegraphy. Waves 
have to be emitted in the same way with this difference; 




Pig. 168. Pig. 169. 

[Reproduced from Electrical Engineering of May 30, 1907, by permission of the 

Proprietors.] 

the strength of the waves must be capable of fluctuation 
caused by a human voice or other varying sound. More¬ 
over, the fluctuations must be considerable, they must 
immediately follow the variations of sound, and they must 
vary in a corresponding manner. Ruhmer discovered 
that the ordinary microphonic telephone transmitter 























250 


RADIO-TELEGRAPHY. 


answered the purpose of varying the vibrations in the 
required manner. The microphone consists of a number 
of loose contacts between carbon granules and metal, in 
circuit with a primary battery. A voice causes varying 
vibrations of the air on the carbons, which correspondingly 
alters the resistance of the contacts and the current in the 
circuit. Puhrner placed the microphone as shown in 
Fig. 168, and he found that the slight variations of current, 
caused by speaking into the transmitter, produced large 

variations of current in the arc 
circuit. He used the receiver 
connexion shown in Fig. 169. 

Fessenden's System of Radio - 
telephony. — Professor Fessenden 
has been working on the solution 
of this problem since 1908, and had 
actually spoken over 25 miles in 
1905. His latest stations have been 
recently described in The Electrician. These are at Brant 
Bock, near Boston, and New York City, a distance apart of 
200 miles, mostly over land. The working connexions are 
shown diagrammatically in Fig. 170. Sustained oscillations 
are produced by an alternator A having a frequency of 81,700 
periods per second. This alternator is of the type described 
on p. 92. The sound transmitter T, is placed directly in 
series with the alternator and aerial, which is 200 feet in 
height. The alternator sets up an oscillatory current of 
5 amperes in this aerial when sending. What Fessenden 


\|/ 


V 




R 

w\ 



£ 


Transmitter. Receiver. 
Fig. 170. 












RADIO-TELEPHONY. 


251 


calls the radiation resistance is 6 to 8 ohms. This radia¬ 
tion resistance appears to be the equivalent of the constant 
56 in Duddell and Taylor’s experiments. There is a local 
telephone exchange with wires both at Brant Rock and 
New York, and the radio-telephone is brought into opera¬ 
tion by a relay R, the same type being used for both 
sending and receiving. This relay is claimed to amplify 
speech 15 times without loss of distinctness. In the 
words of Fessenden, “it consists of a double differential 
magnetic circuit with a pivoted armature to which is 
attached a spade of thin platinum iridium, which dips 
into a trough containing carbon powder, the sides of the 
troughs being formed of platinum iridium sheet.” 

Professor Fessenden has great faith in the future of 
this latest technical development, and he considers that 
10 k.w. only is necessary, with 600 feet masts at either 
end, for transatlantic radio-telephony. 

The Telefunken System of Radio-telephony .—Die Gesell- 
schaft fur drahtlose Telegraphie have kindly furnished the 
author with the following particulars of their system, which 
is working between Berlin and Nauen, a distance of 12 miles. 

Continuous vibrations are produced by means of the 
direct-current arc arranged in conjunction with an 
oscillatory system, connected in parallel with the arc, 
and containing capacity and inductance. These vibrations 
have a frequency corresponding to the oscillation period of 
the circuit, and continue uninterruptedly and with constant 
strength for any length of time, varying only by a fraction 


252 


RADIO-TELEGRAPHY. 


of 1 per cent. The antenna is coupled magnetically with the 
inductance coil of the oscillating circuit; the energy supplied 
through the coupling of the antenna is controlled by a 
specially constructed microphone, which reproduces speech. 

The words are received or heard by means of the 
Schlomilch detector and telephone. The connexion of the 
receiver is similar to that in radio-telegraphy. Fig. 171 
shows a complete radio-telephone apparatus. 

The connexion to the direct-current supply is made by 
means of the switchboard at the right of the apparatus 
table. The dynamo leads are taken to the main switch, 
placed at the edge of the table at the back, on the left-hand 
side, then to the regulating resistance mounted at the side 
of the table, and from this to the choking coils arranged 
under the table, with and without iron core, and thence to 
a direct-current ammeter, fastened to the wall at the back 
of the table, and from this to the arc. Six arcs are connected 
in series, which require a working pressure of 220 volts 
and a direct current of 4 amperes. The arcs are formed 
between a carbon electrode 30 mm. diameter and a cooled 
copper tube 45 mm. diameter. Their length is controlled by 
fine threaded screws. Each pair of electrodes can be brought 
together independently, but the whole series can be separated 
simultaneously by the action of a single lever. The carbons 
are consumed very slowly, so that it is only occasionally neces¬ 
sary to reduce the length of the arc by means of the screw 
adjustment. The bottoms of the cylinder-shaped vessels, 
which hold water for cooling, form the copper electrodes. 


RADIO-TELEPHONY 


253 



Fig. 171 











































254 


RADIO-TELEGRAPHY. 


The oscillating circuit contains a condenser to the left of 
the lamps, a hot-wire ammeter over the condenser, the arcs, 
and an inductance coil to the right under the table. The 
wave lengths can be varied, by altering the condenser, from 
300 to 800 metres. 

By the side of the inductance coil in the oscillating circuit 
may be seen another coil with a few windings, which serves 
to couple the closed circuit to the antenna. Above the 

table the microphone and the 
speaking funnel are arranged. 
The antenna circuit also con¬ 
tains a hot-wire ammeter on 
the left of the table, which 
shows the changes in the cur¬ 
rent from the antenna under 
the influence of the micro¬ 
phone. The switch in the 
middle of the table is used for 
changing from “ speaking ” to “ hearing.” A movement 
with the hand is sufficient to interrupt the high-frequency 
oscillating circuit, to switch the antenna from “trans¬ 
mitting” to “receiving,” and to switch on the receiving 
apparatus. 

Whilst working the station the telephone is held to the 
ear, so that between question and answer it is only neces¬ 
sary to move the switch from right to left. 

By the side of the revolving condenser in the middle of 
the table is the receiving apparatus, resting on an ebonite 



[Reproduced from Electrical Engineering 
of Jan. 31, 1907, by pernrssion of the 
Proprietors. ] 

































RADIO-TELEPHONY. 


255 


plate on four porcelain insulators ; it contains the Schld- 
milch detector with adjusting apparatus and accessories 
and plugs for the telephone. To the left of the receiving 
apparatus stands a variometer, an apparatus with two 
inductance coils placed one inside the other, whose relative 
position may be varied by rotation. The antenna and the 
receiving circuit are tuned to the in¬ 
coming oscillations by means of the 
variometer. 

Other Systems .—Vreeland has used 
a modification of the Cooper-Hewitt 
mercury rectifier for producing sus¬ 
tained waves. It will be seen from 
Fig. 172 that the aerial is separated 
from the closed oscillatory circuit by 
a third circuit containing a micro¬ 
phone. The alterations of resistance 
due to speaking into this telephone transmitter varies the 
current, thus causing varied strength of oscillations in the 
aerial. 

Two methods have been patented by De Forest. In one 
(Fig. 178) he uses an alternator having a periodicity of at 
least 750 cycles a second. In the closed circuit is placed a 
spark-gap, and in the aerial is a resistance device easily 
varied by the action of the voice. For this device De Forest 
uses (1) the microphone ; (2) a flame made conducting by 
sodium salts; or (8) a jet of compressed air impinging on 
a spark-gap with a megaphone, acting on a valve to alter 














256 


RADIO-TELEGRAPHY. 


the flow of air. In the second method De Forest uses 
direct current with a Duddell arc in the aerial circuit, the 
current through the arc being directly affected by a 
megaphone. All the men-of-war of the United States 
Navy have been fitted with radio-telephone apparatus on 
the De Forest system. 

The Amalgamated Radio-Telegraph Company are experi¬ 
menting with the Poulsen arc between Oxford and Cam¬ 
bridge, having succeeded in their first trials over a few 
miles, but no technical information is available. 


* 


APPENDIX A. 

-♦- 

THE MORSE ALPHABET. 

A - — N — - 

B — - - - O- 

C — - — - P-- 

d — . - a-- — 

E - R- 

F- S - - - 

Gr- T — 

H- U- 

I - - V - - - — 

J - -- W- 

K- X- 

L- Y —- 

M- Z- 

3---- 8- 

Abbreviations used by the Anglo-American Telegraph 

Company, Limited. 

Full stop (.). 

Comma (,) -- 

Hyphen (-) —- 

After conclusion of message - - - — - 
Signal between address and text - - 
Repeat - --- 

Engaged on other circuit — —-- — 

Parenthesis — --- — 

Inverted commas - — - - —- - 
Zero (0) — 

Underline - - — — - —■ 

Clear — - — - 


R.T. 


s 




258 


RA1 )I0-TELEGRAPHY. 


Abbreviations adopted at the International Radio¬ 
telegraphic Conference of Berlin, 1906. 


Ships in distress signal . 

A wish to communicate by inter¬ 
national code of signals ; after ■ - — — - - — - — - - - 
the call-signal signal . . . / 



. — - — - —■ (call signal of coast 
For a ship station to call a coast | station 3 times); — - - - 


station signal 


The coast station called answers 


| (call signal of transmitting 

' station 3 times) 

^ — - — - — (call signal of ship 
( station 3 times); — ... 
j (call signal of coast station 

3 times) —- - — 


Invitation to transmit . . . - 

The commencement of a radio- ) 
telegram . . . . . j 

The completion of a radio-telegram | 


After signalling 20 words of a } 
radio-telegram signal . . ) 

The transmitting station then \ 
awaits the last word from the ' - 
receiving station, followed by . J 
At the completion of work each ) 
station signals . . . . j 


— - — - (call signal of trans¬ 
mitting station) 


APPENDIX B. 


The 

The 

The 

The 

The 

The 

The 

The 

The 

The 

The 

The 

The 

The 


-♦- 

ELECTRICAL UNITS USED IN THIS BOOK. 

volt = The unit of electro-motive force or potential 

difference. 

millivolt = One thousandth (10 - 3 ) of a volt, 

microvolt = One millionth (10 ~ 6 ) of a volt, 

ampere = The unit of electric current, 
milliampere = One thousandth (10 -3 ) of an ampere, 
microampere = One millionth (10 ^ 6 ) of an ampere, 
ohm = The unit of resistance, 

megohm = One million (10'’) ohms, 
microfarad = The unit of capacity, 
centimetre = The electrostatic unit of capacity. 

= The electro-magnetic unit of inductance, 
henry = The practical unit of inductance. 

= One thousand million (10 ) centimetres, 
millihenry = One thousandth (10 _3 ) of a henry, 
watt = The unit of power. 

= 755th of a horse-power, 
kilowatt = One thousand watts. 


Note.—A ll the units mentioned are electro-magnetic with the 
exception of the electrostatic unit of capacity. 



APPENDIX C. 


INTERNATIONAL CONTROL OF RADIO¬ 
TELEGRAPHY. 

In 1903 a Preliminary Wireless Telegraph Conference 
was held at Berlin, and this was followed in 1906 by the 
International Radio-telegraphic Conference of Berlin, whilst 
a third is arranged to be held in London during 1911, so 
that it appears likely that they will become quintennial, as 
in the case of the Telegraphic Conferences. 

The necessity for international arrangement was ably 
put forward by H. G. M. Krsetke, Secretary of State for the 
Postal Department of the German Empire, in his opening 
address at the last Conference, when he pointed out that 
the electromagnetic waves were not confined within the 
frontiers of the State producing them even when the 
receiving station was situated within the State. 

The principal question for discussion at Berlin was 
compulsory communication between ship and coast stations. 
The majority of the Powers wished to make intercommuni¬ 
cation compulsory without reserve, but Mr. Babington 
Smith, Secretary of the General Post Office of Great Britain, 



APPENDIX C. 


261 


pointed out the confusion that was likely to arise. Some 
stations have been erected especially to keep in touch with 
passenger steamers making short passages, such as across the 
English Channel; at other points, where numerous ships 
meet, great congestion must take place with unrestricted com¬ 
munication, and division of traffic is indispensable. Again, 
a system may be invented which could only communicate 
with stations employing the same system. On these 
grounds Great Britain held that certain stations should be 
permitted which gave a service of a restricted character. 
Great Britain also held that other coast stations might be 
erected which were exempt from intercommunicating with 
others, though, in this case, extra stations would be pro¬ 
vided. Great Britain finally won her contention, though, 
in the final protocol, eighteen countries declared that they 
would not reserve the power of erecting specially exempted 
stations. 

Thus, according to the convention, coast stations may be 
divided as follows :— 

(1) Those used for general public correspondence with 

ships; 

(2) Those with a restricted service; 

(8) Specially exempted stations ; 

(4) Military and naval stations ; 

(5) Coast to coast stations. 

The last named were not dealt with by the Conference, 
whilst military and naval stations were exempted from the 
terms of the convention, except in that they must interfere 


262 


RADIO-TELEGRAPHY. 


as little as possible with other stations, and give priority to 
calls of ships in distress. 

Though not in the original draft, the question of ship to 
ship stations also came up, and an additional undertaking, 
providing for compulsory intercommunication, was signed 
by twenty-one countries, Great Britain not being amongst 
them. 

To make intercommunication possible between stations 
wave-lengths had to be decided. Every coast station has 
to employ one of two waves—300 or 600 metres—and it 
must always be in a position to receive calls made with its 
own wave-length ; also it must always make use of its own 
wave for general public correspondence. For special 
purposes waves not exceeding 600 metres or exceeding 
1,600 metres may be used ; between these limits the wave¬ 
lengths are reserved for naval and military stations. Every 
ship station, with the exception of those of small tonnage, 
has to use a normal wave-length of 300 metres, but other 
waves may be ‘also used provided they do not exceed 600 
metres. 

To avoid interference ships under normal circumstances 
must not use power plant exceeding one kilowatt, and for 
efficient working the speed of signalling is fixed at twelve 
words a minute ; telegraphists must hold Government 
certificates as to their competency, and he capable of trans¬ 
mitting and receiving by sound at the rate of twenty words 
a minute. 

The Service Regulations also deal with the hours of 


APPENDIX C. 


203 


service, the maximum charges to he levied with method of 
collection, the transmission and delivery of radiograms, 
records to he kept, refunds, accounts, the functions of 
the International Bureau, as well as miscellaneous pro¬ 


visions. 



INDEX 


♦ 


A. 

Aerial, capacity of, 96 

closed circuit, 116 
construction, 119—126, 
225—227 

coupled to a closed cir¬ 
cuit, 95, 99, 101 —114, 
147—153, 207,211, 212 
De Forest, 104, 120, 153 
disadvantages of a single, 
96 

earthing the, 61, 123— 
127, 227 
horizontal, 115 
loaded with cajiacity, 95, 
98, 215, 241 

Marconi’s, 61, 94, 95, 
123, 243 

material used in, 119, 120 
Nauen, at, 226 
Pierce’s experiments, 64 
Poldhu, at, 101 
portable stations, for, 
240—248 

receiving, 146, 153 
Scheveningen, at, 123 
sending, 95, 98, 100 
ships, for, 101 
Tralee, at, 239 
trees as, /1 


Aether, 56 

Air, ionisation of, 72, 133 
Algermissen, J., 133 
Alternate current transformers, 
83 

Alternators, 83, 84 

high frequency, 92, 255 
Amalgamated Radio-Telegraph 
Company, 104, 121, 232, 256 
Ammeter, 186, 192 
Ampere, 15, 42, 259 
Amplitude, 

electric vibrations, of, 32, 40 
in receiver, 152, 158 
in transmitter, 105 
vibrations, of, 25—27 
waves, of, 46, 47, 57 
Anchor spark, 128 
Antenna, 100 
Antinode, 27, 32, 40 
Apparatus, arrangement of, 141 
charging the oscilla¬ 
tor, for, 76—93 
protection of, 87, 127, 
231 

Arc, compressed air, in, 93 

musical, 87, 141—144, 232— 
239 

Telefunken, 252 
Arcing at spark-gap, 82, 136 
Aschkinass, A., 174 





266 


INDEX. 


Audion, 172 

Austin, L. W., 93, 177 

Auto-coherer, 171 

Auto-transformer, receiving, 149 

sending, 112 
Auto-transmitter, 140 


B. 

Barretter, 176, 197 
Bellini, E., 95, 116 
Bjerknes, V., 59 
Bolometer, 196 
Brandes, II., 177 
Branly, E., 60, 145, 163 
Braun, E., coupled systems, 94, 
113 

directive wave sys¬ 
tem, 115 

screening action of 
obstructions, 71 
Brown, A. C., 175 

C. 

Calling-up arrangement, 180 
Capacity, 

aerial, of, 96 
definition of, 9 
mechanical analogue, 33 
oscillatory circuits, of, 32, 98, 
100, 103, 114, 204, 210 
shunt to a battery, 155 
a detector, 152 
an induction cord, 78 
a transmitting key, 
78, 139 

variation of spark with, 130 


Carborundum detector, 177 
Castelli, Signor, 163, 171 
Charges, 

electric, 1, 5, 7, 12, 23, 31, 
33 

definition of, 1 
moving, 37, 63 
properties of, 3 

Choking coils, 104, 143, 155, 231 
Circuits, 

for charging oscillator, 78, 
84, 86 

oscillatory, Hertz’s, 48 

open and closed, 
59, 109 
secondary, 39 
potentiometer, 180 
receiver, 145—162, 203, 204 
transmitter, 94—118, 186— 
192 

Coherers, 165, 166, 168 
Compliancy, 30 
Condenser, definition of, 9 
field of force, 6 
Leyden jar, 10, 59, 
137, 141 

Nauen, at, 228, 231 
receiver circuits, in, 
153, 157, 161, 236 
sending circuits, in, 
103, 104 

wavemeter circuit, in, 
198, 204 

Conductors, 2, 6 

Coupled circuits, resonance curves 
of, 207 

Coupling, best, 191, 209 

close and loose defined, 
101 

directive circuits, of, 118 




INDEX. 


267 


Coupling, Duddell and Taylor’s 
experiments on ,191 
liigli power station, of, 
86 , 113 

limitation of close, 108, 
137 

measurement of, 208, 
209 

methods of, 103, 137 
receiving circuits, of, 
147, 160 

sending circuits, of, 99 
Currents, electric 

conduction, 15, 18 
defined, 14, 15, 37, 38 
density, 191 
detectors, 172 
displacement, 14, 17 
measurements, 187, 
192 

measuring instru- 
ments, 192—198 
mechanical analogy, 
33 

penetration of, 18,191 
production of, 17, 22 
properties of, 15 
vibratory, 31 

Curvature of the earth, 68 
Cymometer, 200 

D. 

Damping, closed circuits, of, 34,59 
coupled circuits, of, 
108, 211 
curve, 211 

decrement, 59, 210, 239 
defined, 26 

electric vibrations, of, 
30, 35, 5 i 


Damping, factor, 59 

Hertz oscillator, in, 59 
open circuits, in, 97, 
104 

receiving circuits, in, 
152 

Daylight, 72 
De Forest, aerial, 153 

alternator, use of, 76 
anchor spark, 128 
audion, 172 
apparatus, 141 
electrolytic detector, 
17o 

radio-telephone sys¬ 
tem, 255 
De Laval turbine, 92 
Detector, audion, 172 

barretter, 176 
carborundum, 177 
electrolytic, 174 
lead peroxide, 175 
magnetic, 172 
microphonic, 177 
telephone as a, 178 
thermo-electric, 177 
Detectors, compared, 179 
current, 172 
potential, 165 
testing, 180 
Dielectric, 2, 5, 10, 11 
Dimensions of electric quantities, 
24 

Diplex working, 149, 224 
Directed waves, 

Bellini and Tossi, 116 
Braun, 115 
Garcia, 114 
Marconi, 114, 115 
Displacement, 11, 12, 14 







268 


INDEX. 


Donitz, J., wavemeter, 198 
Drude, P., damping, on, 98, 211 
wave-length, on, 209 
Duddell, W., arc, 88 

thermo - galvano - 
meter, 194 

Duddell and Taylor, experiments 
on, 

best coupling, 191 
earthing arrangements, 126 
energy received, 73 
radiation of received vibra¬ 
tions, 152 

resistance of measuring in¬ 
struments, 189 
screening action, 70 
Dunwoody, General, 178 
Duration of vibrations, 56, 91 
Dynamometer, high frequency, 
198 

Dissipation of energy, 72 
E. 

Earth connexion, 

experiments on best, 126 
first used, 60 

Lodge - Muirhead arrange¬ 
ment, 62, 127, 216, 241 
Marconi and Fessenden, ] 26 
Nauen, at, 227 
Telefunken portable stations, 
for, 246 

Earthed Hertzian waves, 63, 66 
Eccles, W. IL, 167, 173 
Elasticity, 33, 45 

Electric field, 4, 6, 7, 14, 16, 52, 
54, 56, 62 

force, 4, 5, 9, 14, 49 
inertia, 18,20, 32, 33, 209 


Electric intensity, 5, 6, 9, 11 
thermometer, 193 
units, 23, 259 

Electricity, 1, 13, 20, 21, 52 
Electrolytic detector, 174 
Electro-magnetics, 14 
Electromotive force, 19 
Electro-statics, 14 
Elmers End station, 215—224 
Elster, Professor, 72 
Energy, 22, 28, 72, 73 
Evans, Lieut. LL, 126 
Ewing, J. A., 79 

Electrical Engineering, 117, 122, 
239 

Electrician, The, 55 
E. 

Faraday, M., 42 
Feddersen, B. W., 31, 43, 59 
Fessenden, R., 
alternator, 92 
barretter, 176, 197 
earthing arrangements, 126 
electrolytic detector, 175 
radio-telephone system, 250 
spark-gap, 135 
use of long waves, 72 
Fleming, J. A., 

audion detector, 172 
best coupling, 209 
cymometer, 200 
electric vibrations, 40 
high-power apparatus, 86 
material of spark-knobs, 135 
measurement of train of 
waves, 214 

number of oscillations, 213 
Poulsen arc, 88 




INDEX. 


269 


G. 

Garcia, M. R., 114, 146 
Gavey, J., 70 
Geissler tube, 39 
Geitel, J. von, 72 
Gutlie, K. E., 166, 167 

H. 

Hammer interrupter, 80 
Harmonics, 27, 40 
Heaviside, Oliver, 33 
Hertz, H., discoverer of radio¬ 
telegraphy, 43 
experiments, 48—56 
wave - lengths em¬ 
ployed, 58 
waves, 59, 65 
velocity of waves, 47 
Heydweiller, A., 133 
High-power apparatus, 85 
History, 42, 60, 76, 94, 145, 163 
Hughes microphone, 177 
Hydrogen arc, 141 

I. 

Inductance, 33 
Induction, 3 

coil, 76—83 
mutual and self, 20 
Insulators, 2, 10, 11, 119 
Interference, 28 

J. 

Jackson, Rear Admiral Sir H. B., 
69 

Jervis-Smith, Rev. F., 135 


L. 

Lampa, A., 58 
Lead peroxide detector, 175 
Leyden jar, 11, 59, 137, 141 
Light, 58, 72 

Lightning, protection from, 127 
Lines of force, 6, 7 
Lodge, Sir Oliver, 

capacity aerial, 94, 153, 212, 
215 

earthing aerial, 66 
energy received, 74 
overflow receiving circuit, 158 
receiving transformer, 145, 
147 

spark, 131, 133 
valve, 83 
Lodge-Muirhead, 
aerial, 98 

auto-transmitter, 140 
calling-up arrangement, 180 
coherer, 168 

earthing arrangements, 98 
leading-in insulator, 123 
portable station, 240 
spark-gaps, 134 
syphon recorder, 157 
system, 215—224 
transformer, 84 
Lyngby station, 232—239 


M. 

Magnetic, detector, 172 

field, 13, 14, 17, 51, 54, 
56 

induction, 13 
Magnetism, 12, 21 






270 


INDEX. 


Marconi, G., 

action of daylight, on, 72 
aerial, 61, 94 
coherer, 167 
directed waves, 114 
earthing arrangements, 126 
Leyden jars, 11 
magnetic detector, 172 
oscillator, 60 
portable stations, 242 
receiving transformer, 145, 
147, 148 
spark-gap, 133 
transatlantic stations, 144 
transmitting key, 139 
Maskelyne, N., 122 
Maxwell, Clerk, 43, 47 
Measuring, coupling, 190, 208 

current in sending 
circuit, 186 
damping, 211 
instruments, 192 
wave-length, 192, 198 
Mercury interrupter, 89, 91 
Microampere, 259 
Microfarad, 9, 259 
Microphonic detector, 177 
Millihenry, 259 
Morse alphabet, 257 
inker, 155 

Muirhead, Alexander, 66 
Multiple coupled circuits, 114 
Multiplicator, 202 
Munk af Rosenschceld, 163 
Murray, Erskine, 64 
Mutual induction, 20, 209 

N. 

Nauen station, 215 
Neon gas, 41 


Neugschwender, 174 
Nodes, 27, 32, 40 

O. 

Obstructions to waves, 68, 70 
Oerstedt, H. C., 42 
Ohm, 18, 259 
Ondameter, 198 
Open oscillation circuit, 95 
Oscillation constant, 36, 148, 205 
Oscillator, electric vibrations 
along, 31 
forms of, 59 
Hertz, 48 

methods of arrange- 
ment, 94—118 
practical details, 119— 
144 

Oscillatory discharge, 2, 31 
Overflow arrangement of Lodge, 
158 

P. 

Period, 25 
Pedersen, P. O., 160 
Pendulum, 25 
Permeability, 13, 20, 24 
Phase, 29 

Pierce, George W., 

action of earthing aerial, 64 
Cooper Ilewitt mercury dis¬ 
charger, on, 89 
couplings, on, 108, 206—208 
distance of signalling, 61 
high frequency dynamo¬ 
meter, 198 

oscillatory transformers, on, 
113 

Polarisation, 13 
Poldhu station, 72 



INDEX. 


271 


Popoff, Professor, 60 
Portable stations, 240—248 
Potential, 7, 19, 31, 32, 33 
detectors, 165 
Potentiometer, 180 
Poulsen, V., arc, 88, 141—144 

radio-telephone sys¬ 
tem, 256 

system, 232—238, 
248 

Ponlsen-Pedersen receiving cir¬ 
cuit, 160—162 
Power-factor, 219 
Preece, Sir "William, 60 
Propagation of waves, 50, 63 
Protection of apparatus, 87, 127 

R. 

Radiating circuit, 100 
Radiation, 35, 47—59, 63 
resistances, 190 
Radio-telephony, 249 
Rayleigh, Lord, 79, 213 
Receiving circuit, 
damping in, 152 
De Eorest arrangement, 153 
Hertz’s, 48 
Lodge’s, 147, 158 
Lodge-Muirhead, 157, 223 
Marconi’s, 147 
measurements, 203 
measuring instruments for, 
194, 196 

necessity of syntony in, 47, 
52, 53, 148, 150 
Popoff, 145 

Poulsen-Pedersen, 160, 238 
secondary, 147, 151 
Slaby, 149 
Telefunken, 229 


Receiving circuits compared, 158 
Receiving transformer, 145, 147 
Recorder, 157 
Relay circuits, 155 
Resistance, 18, 33, 213 
Rempp, Gr., 130 
Resonance, 48, 52 
curve, 205 
Righi, A., 133 
Ross, O. C., 55 
Ruhmer, E., 249 
Rutherford, E., 172 

S. 

Schlomilch detector, 175, 252 
Screening, 70 

Secondary circuits, 99—114, 147, 
151, 192 
vibrations, 37 

Self induction, 18, 20, 32, 33, 209 
Simon, H. Th., 89 
Slaby, A., 133, 149, 202 
Spark, 31, 90, 128, 130, 131, 133, 
135 

Specific inductive capacity, 10, 11, 
24 

Squier, S. O., 71 
Subsidiary circuits, 154 
Sullivan, H. W., 
interrupter, 80 
relay, 182 
Switches, 159 

Syntony, 28, 47, 52, 53, 94, 148, 
150 

T. 

Taylor, J. E., 70, 73, 126, 152, 
189, 190 
Telefunken, 

aerial, 123, 225 



272 


INDEX. 


Telefunken— continued. 
apparatus, 231 
auto-transformer, 149 
coherer, 175 
condenser, 228 
earthing arrangements, 227 
induction coil, 80 
portable stations, 245 
radio-telephone system, 251 
receiving apparatus, 157 
spark-gap, 134 
station at Nauen, 225—231 
transmitting key, 139 
wave-meter, 198, 202 
Telephone, 162 
Tesla transformer, 112 
Thermo-electric detectors, 177 
Thermo-galvanometer, 194 
Thomson, Elihu, 87 
Thomson, J. J., 

Ticker, 161, 237 
Tissot, 0., 73, 152, 189, 196 
Tosi, A., 95, 116 
Tralee Station, 239 
Transformers, 83 
Transmitting, 95 
key, 137 

Trees as aerials, 71 
Trowbridge, J., 167 
Tubes of force, 6, 12, 14 
radiated, 49—56, 63 

U. 

Units, 23, 259 

Y. 

Variometer, 255 
Velocity, charges along wires, of, 
41 


Velocity, waves of, 47, 56 

Vibrating receiver, 47 
string, 27, 30 

Vibrations, damping of, 26 
definition of, 25 
electric, 31, 33 
energy of, 28, 47 
examination of, 39 
principal, 28 
secondary, 37, 39 

Volt, 8, 259 

Vreeland, E. IV, 91, 255 
W. 

Wave-length, 45, 55, 58 

Wave measurement, 198—205 

Waves, advantage of long, 72 
amplitude of, 46 
definition of, 44 
directed, 114 
earthed, 62, 66 
electro-magnetic, 47, 52, 
60 

principal, 106 
stationaiy, in wires, 36 
velocity of propagation of, 
45—47 

Wildman, L. D., 72 

Z. 

Zenneck, J., 

damping of secondary vibra¬ 
tions, 105 

damping of single aerial, 97 

coupling, 137 

wave measurement, 198 


BRADBURY, AONEW, & CO. LD., PRINTERS, LONDON AND TONBRIDGE. 





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List of Contents : Introduction. The Generation and Distri¬ 
bution of Power. The Electric Motor. The Application of 
Electric Power. Electric Power in Collieries. Electric Power 
in Engineering Workshops. Electric Power in Textile Factories. 
Electric Power in the Printing Trade. Electric Power at Sea. 
Electric Power on Canals. Electric Traction. The Overhead 
System and Track Work. The Conduit System. The Surface 
Contact System. Car Building and Equipment. Electric Rail¬ 
ways. Glossary. Index. 

The majority of the allied trades that cluster round the business of 
electrical engineering are connected in some way or other with its power 
and traction branches. To members of such trades and callings, to 
whom some knowledge of applied electrical engineering is desirable 
if not strictly essential, the book is particularly intended to appeal. 
It deals almost entirely with practical matters, and enters to some 
extent into those commercial considerations which in the long run 
must overrule all others. 



THE “ WESTMINSTER ” SERIES 


Town Gas and its Uses for the Production of 

Light, Heat, and Motive Power* By W. H. Y. 

Webber, C.E. With 71 Illustrations. 

List of Contents : The Nature and Properties of Town Gas. The 
History and Manufacture of Town Gas. The Bye-Products of 
Coal Gas Manufacture. Gas Lights and Lighting. Practical 
Gas Lighting. The Cost of Gas Lighting. Heating and Warm¬ 
ing by Gas. Cooking by Gas. The Healthfulness and Safety 
of Gas in all its uses. Town Gas for Power Generation, including 
Private Electricity Supply. The Legal Relations of Gas Sup¬ 
pliers, Consumers, and the Public. Index. 

The “ country,” as opposed to the “ town,” has been defined as 
“ the parts beyond the gas lamps.” This book provides accurate 
knowledge regarding the manufacture and supply of town gas and its 
uses for domestic and industrial purposes. Few people realize the 
extent to which this great industry can be utilized. The author has 
produced a volume which will instruct and interest the generally well 
informed but not technically instructed reader. 

Electro-Metallurgy* By J. B. C. Kershaw, F.I.C. With 
61 Illustrations. 

Contents : Introduction and Historical Survey. Aluminium. 
Production. Details of Processes and Works. Costs. LTtiliza- 
tion. Future of the Metal. Bullion and Gold. Silver Refining 
Process. Gold Refining Processes. Gold Extraction Processes. 
Calcium Carbide and Acetylene Gas. The Carbide Furnace and 
Process. Production. Utilization. Carborundum. Details of 
Manufacture. Properties and Uses. Copper. Copper Refin¬ 
ing. Descriotions of Refineries. Costs. Properties and Utiliza¬ 
tion. The Elmore and similar Processes. Electrolytic Extrac¬ 
tion Processes. Electro-Metallurgical Concentration Processes. 
Ferro-alloys. Descriptions of Works. Utilization. Glass and 
Quartz Glass. Graphite. Details of Process. Utilization. Iron 
and Steel. Descriptions of Furnaces and Processes. Yields and 
Costs. Comparative Costs. Lead. The Salom Process. The Betts 
Refining Process. The Betts Reduction Process. White Lead Pro¬ 
cesses. Miscellaneous Products. Calcium. Carbon Bisulphide. 
Carbon Tetra-Chloride. Diamantine. Magnesium. Phosphorus. 
Silicon and its Compounds. Nickel. Wet Processes. Dry 
Processes. Sodium. Descriptions of Cells and Processes. Tin. 
Alkaline Processes for Tin Stripping. Acid Processes for Tin 
Stripping. Salt Processes for Tin Stripping. Zinc. Wet Pro¬ 
cesses. Dry Processes. Electro-Thermal Processes. Electro- 
Galvanizing. Glossary. Name Index. 

The subject of this volume, the branch of metallurgy which deals 
with the extraction and refining of metals by aid of electricity, is 
becoming of great importance. The author gives a brief and clear 
account of the industrial developments of electro-metallurgy, in lan¬ 
guage that can be understood by those whose acquaintance with either 

( 4 ) 



THE “ WESTMINSTER ” SERIES 


chemical or electrical science may be but slight. It is a thoroughly 
pi actical woik descriptive of apparatus and processes, and commends 
itself to all practical men engaged in metallurgical operations, as well 
as to business men, financiers, and investors. 

Radio-Telegraphy, By C. C, F. Monckton, M.I.E.E. 
With 173 Diagrams and Illustrations. 

Contents : Preface. Electric Phenomena. Electric Vibrations. 
Electro-Magnetic Waves. Modified Hertz Waves used in Radio- 
Telegraphy. Apparatus used for Charging the Oscillator. The 
Electric Oscillator : Methods of Arrangement, Practical Details. 
The Receiver : Methods of Arrangement, The Detecting Ap¬ 
paratus, and other details. Measurements in Radio-Telegraphy. 
The Experimental Station at Elmers End : Lodge-Muirhead 
System. Radio - Telegraph Station at Nauen : Telefunken 
System. Station at Lyngby : Poulsen System. The Lodge- 
Muirhead System, the Marconi System, Telefunken System, and 
Poulsen System. Portable Stations. Radio-Telephony. Ap¬ 
pendices : The Morse Alphabet. Electrical Units used in this 
Book. International Control of Radio-Telegraphy. Index. 

The startling discovery twelve years ago of what is popularly known 
as Wireless Telegraphy has received many no less startling additions 
since then. The official name now given to this branch of electrical 
practice is Radio-Telegraphy. The subject has now reached a thor¬ 
oughly practicable stage, and this book presents it in clear, concise 
form. The various services for which Radio-Telegraphy is or may 
be used are indicated by the author. Every stage of the subject is 
illustrated by diagrams or photographs of apparatus, so that, while 
an elementary knowledge of electricity is presupposed, the bearings 
of the subject can be grasped by every reader. No subject is fraught 
with so many possibilities of development for the future relationships 
of the peoples of the world. 

India-Rubber and its Manufacture, with Chapters 

on Gutta-Percha and Balata. By H. L. Terry, 
F.I.C., Assoc.Inst.M.M. With Illustrations. 

List of Contents : Preface. Introduction : Historical and 
General. Raw Rubber. Botanical Origin. Tapping the Trees. 
Coagulation. Principal Raw Rubbers of Commerce. Pseudo- 
Rubbers. Congo Rubber. General Considerations. Chemical 
and Physical Properties. Vulcanization. India-rubber Planta¬ 
tions. India-rubber Substitutes. Reclaimed Rubber. Washing 
and Drying of Raw Rubber. Compounding of Rubber. Rubber 
Solvents and their Recovery. Rubber Solution. Fine Cut Sheet 
and Articles made therefrom. Elastic Thread. Mechanical 
Rubber Goods. Sundry Rubber Articles. India-rubber Proofed 
Textures. Tyres. India-rubber Boots and Shoes. Rubber for 
Insulated Wires. Vulcanite Contracts for India-rubber Goods. 

( 5 ) 


THE “ WESTMINSTER ” SERIES 


The Testing of Rubber Goods. Gutta-Percha. Balata. Biblio¬ 
graphy. Index. 

Tells all about a material which has grown immensely in com¬ 
mercial importance in recent years. It has been expressly written 
for the general reader and for the technologist in other branches of 
industry. 


Glass Manufacture* By Walter Rosenhain, Superin¬ 
tendent of the Department of Metallurgy in the National 
Physical Laboratory, late Scientific Adviser in the Glass 
Works of Messrs. Chance Bros, and Co. With Illustra¬ 
tions. 

Contents : Preface. Definitions. Physical and Chemical Qualities. 
Mechanical, Thermal, and Electrical Properties. Transparency 
and Colour. Raw materials of manufacture. Crucibles and 
Furnaces for Fusion. Process of Fusion. Processes used in 
Working of Glass. Bottle. Blown and Pressed. Rolled or 
Plate. Sheet and Crown. Coloured. Optical Glass : Nature 
and Properties, Manufacture. Miscellaneous Products. Ap¬ 
pendix. Bibliography of Glass Manufacture. Index. 

This volume is for users of glass, and makes no claim to be an ade¬ 
quate guide or help to those engaged in glass manufacture itself. For 
this reason the account of manufacturing processes has been kept 
as non-technical as possible. In describing each process the object 
in view has been to give an insight into the rationale of each step, so 
far as it is known or understood, from the point of view of principles 
and methods rather than as mere rule of thumb description of manu¬ 
facturing manipulations. The processes described are, with the 
exception of those described as obsolete, to the author’s definite know¬ 
ledge, in commercial use at the present time. 


Precious Stones. By W. Goodchild, M.B., B.Ch. With 
42 Illustrations. With a Chapter on Artificial 

Stones. By Robert Dykes. 

List of Contents : Introductory and Historical. Genesis of 
Precious Stones. Physical Properties. The Cutting and Polish¬ 
ing of Gems. Imitation Gems and the Artificial Production of 
Precious Stones. The Diamond. Fluor Spar and the Forms of 
Silica. Corundum, including Ruby and Sapphire. Spinel and 
Chrysoberyl. The Carbonates and the Felspars. The Pyroxene 
and Amphibole Groups. Beryl, Cordierite, Lapis Lazuli and the 
Garnets. Olivine, Topaz, Tourmaline and other Silicates. Phos¬ 
phates, Sulphates, and Carbon Compounds. 

An admirable guide to a fascinating subject. 

( 6 )' 




_THE “ WESTMINSTER ” SERIES 

Patents, Designs and Trade Marks : The Law 

and Commercial Usage* By Kenneth R. Swan, 
B.A. (Oxon.), of the Inner Temple, Barrister-at-Law. 

Contents : Table of Cases Cited— Part I .— Letters Patent. Intro¬ 
duction. General. Historical. I., II., III. Invention, Novelty, 
Subject Matter, and Utility the Essentials of Patentable Invention. 
IV. Specification. V. Construction of Specification. VI. Who 
May Apply for a Patent. VII. Application and Grant. VIII. 
Opposition. IX. Patent Rights. Legal Value. Commercial 
Value. X. Amendment. XI. Infringement of Patent. XII. 
Action for Infringement. XIII. Action to Restrain Threats. 
XIV. Negotiation of Patents by Sale and Licence. XV. Limita¬ 
tions on Patent Right. XVI. Revocation. XVII. Prolonga¬ 
tion. XVIII. Miscellaneous. XIX. Foreign Patents. XX. 
Foreign Patent Laws : United States of America. Germany. 
France. Table of Cost, etc., of Foreign Patents. Appendix A.— 
i. Table of Forms and Fees. 2. Cost of Obtaining a British 
Patent. 3. Convention Countries. Part II. — Copyright in 
Design. Introduction. I. Registrable Designs. II. Registra¬ 
tion. III. Marking. IV. Infringement. Appendix B.—1. 
Table of Forms and Fees. 2. Classification of Goods. Part 
III. — Trade Marks. Introduction. I. Meaning of Trade Mark. 
II. Qualification for Registration. III. Restrictions on Regis¬ 
tration. IV. Registration. V. Effect of Registration. VI. 
Miscellaneous. Appendix C.—Table of Forms and Fees. Indices. 
1. Patents. 2. Designs. 3. Trade Marks. 

This is the first book on the subject since the New Patents Act. 
Its aim is not only to present the existing law accurately and as fully 
as possible, but also to cast it in a form readily comprehensible to the 
layman unfamiliar with legal phraseology. It will be of value to those 
engaged in trades and industries where a knowledge of the patenting 
of inventions and the registration of trade marks is important. Full 
information is given regarding patents in foreign countries. 

The Book; Its History and Development* By 

Cyril Davenport, V.D., F.S.A. With 7 Plates and 
126 Figures in the text. 

List of Contents : Early Records. Rolls, Books and Book 
bindings. Paper. Printing. Illustrations. Miscellanea. 
Leathers. The Ornamentation of Leather Bookbindings without 
Gold. The Ornamentation of Leather Bookbindings with Gold, 
Bibliography. Index. 

The romance of the Book and its development from the rude inscrip¬ 
tions on stone to the magnificent de Luxe tomes of to-day have 
never been so excellently discoursed upon as in this volume, the 
history of the Book is the history of the preservation of human thought. 
This work should be in the possession of evey book lover. 

( 7 ) 





Van Nostrand’s “Westminster Series 


LIST OF NEW AND FORTHCOMING 

VOLUMES. 

Timber. By J. R. Baterden, A.M.I.C.E. 

Steam Engines. ByJ. T. Rossiter, M.EE.E., 
A.M.LM.E. 

Electric Lamps. By Maurice Solomon, A.C.G.E, 
A.M.I.E.E. 

The Railway Locomotive. By Vaughan Pendred, 
M.I.Mech.E. 

Leather. By H. Garner Bennett. 

Pumps and Pumping Machinery. By James W. 
Rossiter, A.M.LM.E. 

Workshop Practice. By Professor G. F. Char- 
nock, A.M.I.C.E., M.I.M.E. 

Textiles and their Manufacture. By Aldred Bar¬ 
ker, M.Sc. 

Gold and Precious Metals. By Thomas K. Rose, 

D. Sc., of the Royal Mint. 

Photography. By Alfred Watkins, Past Presi¬ 
dent of the Photographic Convention. 

Commercial Paints and Painting. By A. S. Jen¬ 
nings, Hon. Consulting Examiner, City and Guilds of 
London Institute. 

Ornamental Window Glass Work. By A. L. 

Duthie. 

Brewing and Distilling. By James Grant, F.C.S. 
Wood Pulp and Its Applications. By C. F. Cross, 

E. J. Bevan and R. W. Sindall. 

The Manufacture of Paper. By R. W. Sindall. 


D. VAN NOSTRAND COMPANY 

‘Publishers and booksellers 

23, MURRAY AND 27. WARREN STREETS, NEW YORK. 









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